The Diet-Heart Hypothesis: A Little Perspective

Now that we've discussed the first half of the diet-heart hypothesis, that saturated fat elevated total and LDL cholesterol, let's take a look at the second half. This is the idea that elevated serum cholesterol causes cardiovascular disease, also called the "lipid hypothesis".

Heart Attack Mortality vs. Total Mortality

We've been warned that high serum cholesterol leads to heart attacks and that it should be reduced by any means necessary, including powerful cholesterol-lowering drugs. We've been assailed by scientific articles and media reports showing associations between cholesterol and heart disease. What I'm going to show you is a single graph that puts this whole issue into perspective.
The following is drawn from the Framingham Heart study (via the book Prevention of Coronary Heart Disease, by Dr. Harumi Okuyama et al.), which is one of the longest-running observational studies ever conducted. The study subjects are fairly representative of the general population, although less racially diverse (largely Caucasian). The graph is of total mortality (vertical axis) by total cholesterol level (horizontal axis), for different age groups: If you're 80 or older, and you have low cholesterol, it's time to get your affairs in order. Between the age of 50 and 80, when most heart attacks occur, there's no association between cholesterol level and total mortality. At age 50 and below, men with higher cholesterol die more often. In the youngest age group, the percent increase in mortality between low and high cholesterol is fairly large, but the absolute risk of death at that age is still low. There is no positive association between total cholesterol and mortality in women at any age, only a negative association in the oldest age group.

Here's more data from the Framingham study, this time heart attack deaths rather than total mortality (from the book Prevention of Coronary Heart Disease, by Dr. Harumi Okuyama et al.): Up to age 47, men with higher cholesterol have more heart attacks. At ages above 47, cholesterol does not associate with heart attacks or total mortality. Since the frequency of heart attacks and total mortality are low before the age of 47, it follows that total cholesterol isn't a great predictor of heart attacks in the general population.

These findings are consistent with other studies that looked at the relationship between total cholesterol and heart attacks in Western populations. For example, the observational arm of the massive MRFIT study found that higher cholesterol predicted a higher risk of heart attack in men age 35-57, but total mortality was highest both at low and high cholesterol levels. The "ideal" cholesterol range for total mortality was between 140 and 260 mg/dL (reference). Quite a range. That encompasses the large majority of the American public.

The Association Between Blood Cholesterol and Heart Attacks is Not Universal
The association between total cholesterol and heart attacks has generally not been observed in Japanese studies that did not pre-select for participants with cardiovascular risk factors (Prevention of Coronary Heart Disease, by Dr. Harumi Okuyama et al.). This suggests that total blood cholesterol as a marker of heart attack risk is not universal. It would not necessarily apply to someone eating a non-Western diet.

Subdividing Cholesterol into Different Lipoprotein Particles Improves its Predictive Value

So far, this probably hasn't shocked anyone. Most people agree that total cholesterol isn't a great marker. Researchers long ago sliced up total cholesterol into several more specific categories, the most discussed being low-density lipoprotein (LDL) and high-density lipoprotein (HDL). These are tiny fatty droplets (lipoproteins) containing fats, cholesterol and proteins. They transport cholesterol, fats, and fat-soluble vitamins between tissues via the blood.

The LDL and HDL numbers you get back from the doctor's office typically refer to the amount of cholesterol contained in LDL or HDL per unit blood serum, but you can get the actual particle number measured as well. One can also measure the level of triglyceride (a type of fat) in the blood. Triglycerides are absorbed from the digestive tract and manufactured by the liver in response to carbohydrate, then sent to other organs via lipoproteins.

The level of LDL in the blood gives a better approximation of heart attack risk than total cholesterol. If you're living the average Western lifestyle and you have high LDL, your risk of heart attack is substantially higher than someone who has low LDL. LDL particle number has more predictive value than LDL cholesterol concentration. The latter is what's typically measured at the doctor's office. For example, in the EPIC-Norfolk study (free full text), patients with high LDL cholesterol concentration had a 73% higher risk of heart attack than patients with low LDL. Participants with high LDL particle number had exactly twice the risk of those with low LDL number. We'll get back to this observation in a future post.

In the same study, participants with low HDL had twice the heart attack risk of participants with high HDL. That's why HDL is called "good cholesterol". This finding is fairly consistent throughout the medical literature. HDL is probably the main reason why total cholesterol doesn't associate very tightly with heart attack risk. High total cholesterol doesn't tell you if you have high LDL, high HDL or both (LDL and HDL are the predominant cholesterol-carrying lipoproteins).

Together, this suggests that the commonly measured lipoprotein pattern that associates most tightly with heart attack risk in typical Western populations is some combination of high LDL (particularly LDL particle number), low HDL, and high triglycerides.
In the next post, I'll slice up the lipoproteins even further and comment on their association with cardiovascular disease. I'll also begin to delve into how diet affects the lipoproteins.

The Diet-Heart Hypothesis: Stuck at the Starting Gate?

The diet-heart hypothesis is the idea that (1) dietary saturated fat, and in some versions, dietary cholesterol, raise blood cholesterol in humans and (2) therefore contribute to the risk of heart attack.

I'm not going to spend a lot of time on the theory in relation to dietary cholesterol because the evidence that typical dietary amounts cause heart disease in humans is weak.  Here's a graph from the Framingham Heart study (via the book Prevention of Coronary Heart Disease, by Dr. Harumi Okuyama et al.) to drive home the point. Eggs are the main source of cholesterol in the American diet. In this graph, the "low" group ate 0-2 eggs per week, the "medium" group ate 3-7, and the "high" group ate 7-14 eggs per week (click for larger image): The distribution of blood cholesterol levels between the three groups was virtually identical. The study also found no association between egg consumption and heart attack risk. Dietary cholesterol does not have a large impact on serum cholesterol in the long term, perhaps because humans are adapted to eating cholesterol. Most people are able to adjust their own cholesterol metabolism to compensate when the amount in the diet increases. Rabbits don't have that feedback mechanism because their natural diet doesn't include cholesterol, so feeding them dietary cholesterol increases blood cholesterol and causes vascular pathology.

The first half of the diet-heart hypothesis states that eating saturated fat raises blood cholesterol. This has been accepted without much challenge by diet-health authorities for nearly half a century. In 1957, Dr. Ancel Keys proposed a formula (Lancet 2:1959. 1957) to predict changes in total cholesterol based on the amount of saturated and polyunsaturated fat in the diet. This formula, based primarily on short-term trials from the 1950s, stated that saturated fat is the primary dietary influence on blood cholesterol.

According to Keys' interpretation of the trials, saturated fat raised, and to a lesser extent polyunsaturated fat lowered, blood cholesterol. But there were significant flaws in the data from the very beginning, which were pointed out in this critical 1973 literature review in the American Journal of Clinical Nutrition (free full text).

The main problem is that the controlled trials typically compared saturated fats to omega-6 linoleic acid (LA)-rich vegetable oils, and when serum cholesterol was higher in the saturated fat group, this was most often attributed to the saturated fat raising blood cholesterol rather than the LA lowering it. When a diet high in saturated fat was compared to the basal diet without changing LA, often no significant increase in blood cholesterol was observed. Studies claiming to show a cholesterol-raising effect of saturated fat often introduced it after an induction period rich in LA. Thus, the effect sometimes had more to do with LA lowering blood cholesterol than saturated fat raising it. This is not at all what I was expecting to find when I began looking through these trials.

Reading through the short-term controlled trials, I was surprised by the variability and lack of agreement between them. Some of this was probably due to a lack of control over variables and non-optimal study design. But if saturated fat has a dominant effect on serum cholesterol in the short term, it should be readily and consistently demonstrable.  

The long-term data are not kind to the diet-heart hypothesis. Reducing saturated fat while greatly increasing LA certainly does lower blood cholesterol substantially. This was the finding in the well-controlled Minnesota Coronary Survey trial, for example (14% reduction). But in other cases where LA intake changed less, such as MRFIT, the Women's Health Initiative Diet Modification trial and the Lyon Diet-Heart trial, reducing saturated fat intake had little or no effect on total cholesterol or LDL (0-3% reduction).  The small changes that did occur could have been due to other factors, such as increased fiber and phytosterols, since these were multiple-factor interventions.

Another blow to the idea that saturated fat raises cholesterol in the long term comes from observational studies. Here's a graph of data from the Health Professionals Follow-up study, which followed 43,757 health professionals for 6 years (via the book Prevention of Coronary Heart Disease by Dr. Harumi Okuyama et al.): What this graph shows is that at a relatively constant LA intake, neither saturated fat intake nor the ratio of LA to saturated fat were related to blood cholesterol in freely living subjects. This was true across a wide range of saturated fat intakes (7-15%). 

There's more. If saturated fat were important in determining the amount of blood cholesterol in the long term, you'd expect populations who eat the most saturated fat to have high blood cholesterol levels. But that's not the case. The Masai traditionally get a high proportion of their calories from milk fat, half of which is saturated. In 1964, Dr. George V. Mann published a paper showing that traditional Masai warriors eating practically nothing but very fatty milk, blood and meat had an average cholesterol of 115 mg/dL in the 20-24 year age group. For comparison, he published values for American men in the same age range: 198 mg/dL (J. Atherosclerosis Res. 4:289. 1964). Apparently, eating three times the saturated animal fat and several times the cholesterol of the average American wasn't enough to elevate their blood cholesterol. What does elevate the cholesterol of a Masai man? Junk food.

Now let's swim over to the island of Tokelau, where the traditional diet includes nearly 50% of calories from saturated fat from coconut. This is the highest saturated fat intake of any population I'm aware of. How's their cholesterol? Men in the age group 20-24 had a concentration of 168 mg/dL in 1976, which was lower than Americans in the same age group despite a four-fold higher saturated fat intake. Tokelauans who migrated to New Zealand, eating half the saturated fat of their island relatives, had a total cholesterol of 191 mg/dL in the same age group and time period, and substantially higher LDL (J. Chron. Dis. 34:45. 1981). Sucrose consumption was 2% on Tokelau and 13% in New Zealand. Saturated fat seems to take a backseat to some other diet/lifestyle factor(s).  Body fatness and excess calorie intake are good candidates, since they influence circulating lipoproteins.

Does dietary saturated fat influence total cholesterol and LDL over the long term?  I don't have the answers, but I do think it's interesting that the evidence is much less consistent than it's made out to be.  It may be that if dietary saturated fat influences total cholesterol or LDL concentration in the long term, the effect is is secondary to other factors.  That being said, it's clear that linoleic acid, in large amount, reduces circulating total cholesterol and LDL.

The Finnish Mental Hospital Trial

This diet trial was conducted between 1959 and 1971 in two psychiatric hospitals near Helsinki, Finland. One hospital served typical fare, including full-fat milk and butter, while the other served "filled milk", margarine and polyunsaturated vegetable oils. Filled milk has had its fat removed and replaced by an emulsion of vegetable oil. As a result, the diet of the patients in the latter hospital was low in saturated fat and cholesterol, and high in polyunsaturated fat compared to the former hospital. At the end of six years, the hospitals switched diets. This is known as a "crossover" design.

The results were originally published in 1972 in the Lancet (ref), and a subset of the data were re-published in 1979 in the International Journal of Epidemiology (ref). They found that during the periods that patients were eating the diet low in saturated fat and cholesterol, and high in vegetable oil, male participants (but not females) had roughly half the incidence of heart attack deaths. There were no significant differences in total mortality in either men or women. The female data were omitted in the 1979 report.

This study is often cited as support for the idea that saturated fat increases the risk of heart attack. The reason it's cited so often is it's one of a minority of trials that came to that conclusion. The only other controlled trial I'm aware of that replaced animal fat with polyunsaturated vegetable oil (without changing other variables at the same time) and found a statistically significant decrease in cardiovascular deaths was the Los Angeles Veterans' Administration study. However, there was no difference in total mortality, and there were significantly more heavy smokers in the control group. The difference in heart attack deaths in the V.A. trial was 18%, far less than the difference seen in the Finnish trial.

I can cite three controlled trials that came to the opposite conclusion, that switching saturated fat for vegetable oil increases cardiovascular mortality and/or total mortality: the Anti-Coronary Club Trial (4 years), the Rose et al. corn oil trial (2 years), and the Sydney Diet-Heart trial (5 years). Other controlled trials found no difference in total mortality or heart attack mortality from this intervention, including the National Diet-Heart Study (2 years) and the Medical Research Council study (7 years). Thus, the Finnish trial is an outlier whose findings have never been replicated by better-conducted trials.

I have three main bones to pick with the Finnish trial. The first two are pretty bad, but the third is simply fatal to its use as support for the idea that saturated fat contributes to cardiovascular risk:

1) A "crossover" study design is not an appropriate way to study a disease with a long incubation period. How do you know that the heart attacks you're observing came from the present diet and not the one the patients were eating for the six years before that? The Finnish trial was the only trial of its nature ever to use a crossover design.

2) The study wasn't blinded. When one wants to eliminate bias in diagnosis for these types of studies, one designs the study so that the physician doesn't know which group the patients came from. That way he can't influence the results, consciously or unconsciously. Obviously there was no way to blind the physicians in this study, because they knew what the patients in each hospital were eating. I think it's interesting that the only outcome not susceptible to diagnostic bias, total mortality, showed no significant changes in either men or women.

3) The Finnish Mental Hospital trial was not actually a controlled trial. In an editorial in the November 1972 issue of the Lancet, Drs. John Rivers and John Yudkin pointed out, among other things, that the amount of sugar varied by almost 50% between diet periods. In the December 30th issue, the lead author of the study responded:

In view of the design of the experiment the variations in sugar intake were, of course, regrettable. They were due to the fact that, aside from the fatty-acid composition and the cholesterol content of the diets, the hospitals, for practical reasons, had to be granted certain freedom in dietary matters.

In other words, the diets of the two hospitals differed significantly in ways other than their fat composition. Sugar was one difference. Carbohydrate intake varied by as much as 17% and total fat intake by as much as 26% between diet periods (on average, carbohydrate was lower and total fat was higher in the polyunsaturated fat group). The use of psychiatric drugs with known cardiovascular side effects differed substantially between groups and could have accounted for some of the difference in cardiovascular events.  

The definition of a controlled trial is an experiment in which all variables are kept reasonably constant except the one being evaluated. Therefore, the Finnish trial cannot rightfully be called a controlled trial. The fact that the result has never been replicated casts further doubt on the study.
I could continue listing other problems with the study, such as the fact that the hospital population included in the analysis had a high turnover rate (variable, but as high as 40%), and patients were included in the analysis even if they were at the hospital for as little as 50% of the time between first admission and final discharge (i.e., they came and went). But what's the use in beating a dead horse?

Unrefined vs. Refined Carbohydrates and Dental Cavities

There's a definite association between the consumption of refined carbohydrates and dental cavities. Dr. Weston Price pointed this out in a number of transitioning societies in his epic work Nutrition and Physical Degeneration. Many other anthropologists and dentists have observed the same thing.

I believe, based on a large body of anthropological and medical data, that it's not just an association-- sugar and flour cause cavities. But why? Is it that they lack micronutrients-- the explanation favored by Price-- or do they harm teeth by feeding the bacteria that participate in cavity formation? Or both?

I recently found an interesting article when I was perusing an old copy of the Journal of Dental Research: "A Comparison of Crude and Refined Sugar and Cereals in Their Ability to Produce in vitro Decalcification of Teeth", published in 1937 by Dr. T. W. B. Osborn et al. (free full text). I love old papers. They're so free of preconceptions, and they ask big questions. The authors begin with the observation that the South African Bantu, similar to certain cultures Dr. Price visited, had a low prevalence of tooth decay when eating their native diet high in unrefined carbohydrate foods. However, their decay rate increased rapidly as modern foods such as white flour and refined sugar became available.

To test whether refined carbohydrates have a unique ability to cause tooth decay, the investigators took pieces of teeth that had been extracted for reasons other than decay (for example, crowding), and incubated them with a mixture of human saliva and several different carbohydrate foods:

• crude cane juice
• refined cane sugar
• whole wheat flour
• white wheat flour
• whole corn meal
• refined corn meal

After incubating teeth in the solutions for 2-8 weeks at 37 C (human body temperature), they had trained dentists evaluate them for signs of decalcification. Decalcification is a loss of minerals that is part of the process of tooth decay. Teeth, like bones, are mineralized primarily with calcium and phosphorus, and there is a dynamic equilibrium between minerals leaching out of the teeth and minerals entering them.

The researchers used teeth incubated in saline solution as the reference. The dentists were "blinded", meaning they didn't know which solution each tooth came from. This is a method of reducing bias. Here are some of the results. Cane juice vs. refined sugar:

Unrefined cane juice was not very effective at causing decalcification, compared to refined sugar. This was a surprise to me. Here is the result for wheat:Note that the scale is different on this graph. Wheat, and particularly refined wheat, is very good at decalcifying teeth in vitro. Corn:

Refined corn is much more effective at decalcifying teeth than whole meal corn. Next, the investigators performed an experiment where they compared the three types of refined carbohydrate to one another:
As one would predict from the graphs above, refined wheat is worse than refined corn, is worse than refined sugar. This is really at odds with conventional wisdom.

It's important to keep in mind that these results are not necessarily directly applicable to a living human being, who wouldn't let a mouthful of wheat porridge sit in his mouth for five weeks. But it does show that refining carbohydrates may increase their ability to cause cavities due to a direct effect on the teeth (rather than by affecting whole-body nutritional status, which they do as well).

The authors tested the acidity of the different solutions, and found no consistent differences between them (they were all at pH 4-5 within 24 hours), so acid production by bacteria didn't account for the results. They speculated that the mineral content of the unrefined carbohydrates may have prevented the bacterial acids from leaching minerals out of the teeth. Fortunately for us, they went on to test that speculation in a series of further investigations.

In another paper, Dr. T. W. B. Osborn and his group showed that they could greatly curb the decalcification process by adding organic calcium and phosphorus salts to the solution. This again points to a dynamic equilibrium, where minerals are constantly leaving and entering the tooth structure. The amounts of calcium and phosphorus required to inhibit calcification were similar to the amounts found in unrefined cane sugar, wheat and corn. This suggests the straightforward explanation that refined sugar and grains cause decay at least in part because most of the minerals are removed during the refining process.

However, we're still left with the puzzling fact that wheat and corn flour decalcify teeth in vitro more effectively than cane juice. I suspect that has to do with the phytic acid content of the grains, which binds the minerals and makes them partially unavailable to diffusion into the teeth. Cane juice contains minerals, but no phytic acid, so it may have a higher mineral availability. This explanation may not be able to account for the fact that refined sugar was also less effective at decalcifying teeth than refined wheat and corn flour. Perhaps the residual phytic acid in the refined grains actually drew minerals out of the teeth?

No, I'm not saying you can eat sugar with impunity if it's unrefined. There isn't a lot of research on the effects of refined vs. unrefined sugar, but I suspect too much sugar in any form isn't good. But this does suggest that refined carbohydrates may be particularly effective at promoting cavities, due to a direct demineralizing effect on teeth subsequent to bacterial acid production. It also supports Dr. Price's contention that a food's micronutrient content is the primary determinant of its effect on dental health.

Reversing Tooth Decay
Preventing Tooth Decay
Dental Anecdotes

A Little Tidbit

I'm gearing up for a new series of posts based on some fascinating reading I've been doing lately. I'm not going to spill the beans, but I will give you a little hint, from a paper written by Dr. Robert S. Corruccini, professor of anthropology at Southern Illinois university. I just came across this quote and it blew me away. It's so full of wisdom I can't even believe I just read it. The term "occlusion" refers to the way the upper and lower teeth come together, as in overbite or underbite.

Similar to heart disease and diabetes which are "diseases of civilization" or "Western diseases" (Trowell and Burkitt, 1981) that have attained high prevalence in urban society because of environmental factors rather than "genetic deterioration," an epidemiological transition (Omran, 1971) in occlusal health accompanies urbanization.

Western society has completely crossed this transition and now exists in a state of industrially buffered environmental homogeneity. The relatively constant environment both raises genetic variance estimates (since environmental variance is lessened) and renders epidemiological surveys largely meaningless because etiological factors are largely uniform. Nevertheless most occlusal epidemiology and heritability surveys are conducted in this population rather than in developing countries currently traversing the epidemiological transition.

In other words, the reason observational studies in affluent nations haven't been able to get to the bottom of dental/orthodontic problems and chronic disease is that everyone in their study population is doing the same thing! There isn't enough variability in the diets and lifestyles of modern populations to be able to determine what's causing the problem. So we study the genetics of problems that are not genetic in origin, and overestimate genetic contributions because we're studying populations whose diet and lifestyle are homogeneous. It's a wild goose chase.

That's why you have to study modernizing populations that are transitioning from good to poor health, which is exactly what Dr. Weston Price and many others have done. Only then can you see the true, non-genetic, nature of the problem.

The Coronary Heart Disease Epidemic: Possible Culprits Part I

In the last post, I reviewed two studies that suggested heart attacks were rare in the U.K. until the 1920s -1930s. In this post, I'll be discussing some of the diet and lifestyle factors that preceded and associated with the coronary heart disease epidemic in the U.K and U.S. I've cherry picked factors that I believe could have played a causal role. Many things changed during that time period, and I don't want to give the impression that I have "the answer". I'm simply presenting ideas for thought and discussion.

First on the list: sugar. Here's a graph of refined sugar consumption in the U.K. from 1815 to 1955, from the book The Saccharine Disease, by Dr. T. L. Cleave. Sugar consumption increased dramatically in the U.K. over this time period, reaching near-modern levels by the turn of the century, and continuing to increase after that except during the wars: Here's a graph of total sweetener consumption in the U.S. from 1909 to 2005 (source: USDA food supply database). Between 1909 and 1922, sweetener consumption increased by 40%:

If we assume a 10 to 20 year lag period, sugar is well placed to play a role in the CHD epidemic. Sugar is easy to pick on. Diets high in refined sugar tend to promote obesity due to overeating.  An excess causes a number of detrimental changes in animal models and human subjects that are partially dependent on the development of obesity, including fatty liver, the metabolic syndrome, and small, oxidized low-density lipoprotein particles (LDL). Small and oxidized LDL associate strongly with cardiovascular disease risk and may be involved in causing it. These effects seem to be partly attributable to the fructose portion of sugar, which is 50% of table sugar (sucrose), about 50% of most naturally sweet foods, and 55% of the most common form of high-fructose corn syrup. That explains why starches, which break down into glucose (another type of sugar), don't have the same negative effects as table sugar and HFCS.

Hydrogenated fat is the next suspect. I don't have any graphs to present, because no one has systematically tracked hydrogenated fat consumption in the U.S. or U.K. to my knowledge. However, it was first marketed in the U.S. by Procter & Gamble under the brand name Crisco in 1911. Crisco stands for "crystallized cottonseed oil", and involves taking an industrial waste oil (from cotton seeds) and chemically treating it using high temperature, a nickel catalyst and hydrogen gas (see this post for more information). Hydrogenated fats for human consumption hit markets in the U.K. around 1920. Here's what Dr. Robert Finlayson had to say about margarine in his paper "Ischaemic Heart Disease, Aortic Aneurysms, and Atherosclerosis in the City of London, 1868-1982":

...between 1909-13 and 1924-28, margarine consumption showed the highest percentage increase, whilst that of eggs only increased slightly and that of butter remained unchanged. Between 1928 and 1934, margarine consumption fell by one-third, while butter consumption increased by 57 percent: and increase that coincided with a fall of 48 percent in its price. Subsequently, margarine sales have burgeoned, and if one is correct in stating that the coronary heart disease epidemic started in the second decade of this century, then the concept of hydrogenated margarines as an important aetiological factor, so strongly advocated by Martin, may merit more consideration than hitherto.

Partially hydrogenated oils contain trans fat, which is truly new to the human diet, with the exception of small amounts found in ruminant fats including butter. But for the most part, natural trans fats are not the same as industrial trans fats, and in fact some of them, such as conjugated linoleic acid (CLA), may be beneficial. To my knowledge, no one has discovered health benefits of industrial trans fats. To the contrary, compared to butter, they shrink LDL size. They also inhibit enzymes that the body uses to make a diverse class of signaling compounds known as eicosanoids. Trans fat consumption associates very strongly with the risk of heart attack in observational studies. Which is ironic, because hydrogenated fats were originally marketed as a healthier alternative to animal fats. The Center for Science in the Public Interest shamed McDonald's into switching the beef tallow in their deep friers for hydrogenated vegetable fats in the 1990s. In 2009, even the staunchest opponents of animal fats have to admit that they're healthier than hydrogenated fat.
The rise of cigarettes was a major change that probably contributed massively to the CHD epidemic. They were introduced just after the turn of the century in the U.S. and U.K., and rapidly became fashionable (source):
If you look at the second to last graph from the previous post, you can see that there's a striking correspondence between cigarette consumption and CHD deaths in the U.K. In fact, if you moved the line representing cigarette consumption to the right by about 20 years, it would overlap almost perfectly with CHD deaths. The risk of heart attack is so strongly associated with smoking in observational studies that even I believe it probably represents a causal relationship. There's no doubt in my mind that smoking cigarettes contributes to the risk of heart attack and various other health problems.

Smoking is a powerful factor, but it doesn't explain everything. How is it that the Kitavans of Papua New Guinea, more than 3/4 of whom smoke cigarettes, have an undetectable incidence of heart attack and stroke? Why do the French and the Japanese, who smoke like chimneys (at least until recently), have the two lowest heart attack death rates of all the affluent nations? There's clearly another factor involved that trumps cigarette smoke. 

The Coronary Heart Disease Epidemic

Few people alive today are old enough to remember the beginning of the coronary heart disease (CHD) epidemic in the 1920s and 1930s, when physicians in the U.S. and U.K. began sounding alarm bells that an uncommon disease was rapidly becoming the leading cause of death. By the 1950s, their predictions had come true. A decade later, a new generation of physicians replaced their predecessors and began to doubt that heart attacks had ever been uncommon. Gradually, the idea that the disease was once uncommon faded from the public consciousness, and heart attacks were seen as an eternal plague of humankind, avoided only by dying of something else first.

According to U.S. National Vital Statistics records beginning in 1900, CHD was rarely given as the cause of death by physicians until after 1930. The following graph is from The Great Cholesterol Con, by Anthony Colpo.


The relevant line for CHD deaths begins in the lower left-hand part of the graph. Other types of heart disease, such as heart failure due to cardiomyopathy, were fairly common and well recognized at the time. These data are highly susceptible to bias because they depend on the physician's perception of the cause of death, and are not adjusted for the mean age of the population. In other words, if a diagnosis of CHD wasn't "popular" in 1920, its prevalence could have been underestimated. The invention of new technologies such as the electrocardiogram facilitated diagnosis. Changes in diagnostic criteria also affected the data; you can see them as discontinuities in 1948, 1968 and 1979. For these reasons, the trend above isn't a serious challenge to the idea that CHD has always been a common cause of death in humans who reach a certain age.

This idea was weakened in 1951 with the publication of a paper in the Lancet medical journal titled "Recent History of Coronary Disease", by Dr. Jerry N. Morris. Dr. Morris sifted through the autopsy records of London Hospital and recorded the frequency of coronary thrombosis (artery blockage in the heart) and myocardial infarction (MI; loss of oxygen to the heart muscle) over the period 1907-1949. MI is the technical term for a heart attack, and it can be caused by coronary thrombosis. Europe has a long history of autopsy study, and London Hospital had a long-standing policy of routine autopsies during which they kept detailed records of the state of the heart and coronary arteries. Here's what he found:

The dashed line is the relevant one. This is a massive increase in the prevalence of CHD death that cannot be explained by changes in average lifespan. Although the average lifespan increased considerably over that time period, most of the increase was due to reduced infant mortality. The graph only includes autopsies performed on people 35-70 years old. Life expectancy at age 35 changed by less than 10 years over the same time period. The other possible source of bias is in the diagnosis. Physicians may have been less likely to search for signs of MI when the diagnosis was not "popular". Morris addresses this in the paper:

The first possibility, of course, is that the increase is not real but merely reflects better post-mortem diagnosis. This is an unlikely explanation. There is abundant evidence throughout the forty years that the department was fully aware of the relation of infarction to thrombosis, of myocardial fibrosis to gradual occlusion, and of the topical pathology of ostial stenosis and infarction from embolism, as indeed were many pathologists last century... But what makes figures like these important is that, unlike other series of this kind, they are based on the routine examination at necropsy of the myocardium and of the coronary arteries over the whole period. Moreover Prof. H. M. Turnbull, director of the department, was making a special case of atheroma and arterial disease in general during 1907-1914 (Turnbull 1915). The possibility that cases were overlooked is therefore small, and the earlier material is as likely to be reliable as the later.

Dr. Morris's study was followed by another similar one published in 1985 in the journal Medical History, titled "Ischaemic Heart Disease, Aortic Aneurysms, and Atherosclerosis in the City of London, 1868-1982", conducted by Dr. Robert Finlayson. This study, in my opinion, is the coup de grace. Finlayson systematically scrutinized autopsy reports from St. Bartholemew's hospital, which had conducted routine and detailed cardiac autopsies since 1868, and applied modern diagnostic criteria to the records. He also compared the records from St. Bartholemew's to those from the city mortuary. Here's what he found:

The solid line is MI mortality. Striking, isn't it? The other lines are tobacco and cigarette consumption. These data are not age-adjusted, but if you look at the raw data tables provided in the paper, some of which are grouped by age, it's clear that average lifespan doesn't explain much of the change. Heart attacks are largely an occurrence of the last 80 years.

What caused the epidemic? Both Drs. Morris and Finlayson also collected data on the prevalence of atherosclerosis (plaques in the arteries) over the same time period. Dr. Morris concluded that the prevalence of severe atherosclerosis had decreased by about 50% (although mild atherosclerosis such as fatty streaks had increased), while Dr. Finlayson found that it had remained approximately the same:


He found the same trend in females. This casts doubt on the idea that coronary atherosclerosis is sufficient in and of itself to cause heart attacks, although modern studies have found a strong association between advanced atherosclerosis and the risk of heart attack on an individual level. Heart attacks are caused by several factors, one of which is atherosclerosis.  

What changes in diet and lifestyle associated with the explosion of MI in the U.K. and U.S. after 1920? Dr. Finlayson has given us a hint in the graph above: cigarette consumption increased dramatically over the same time period, and closely paralleled MI mortality. Smoking cigarettes is very strongly associated with heart attacks in observational studies. Animal studies also support the theory. While I believe cigarettes are an important factor, I do not believe they are the only cause of the MI epidemic. Dr. Finlayson touched on a few other factors in the text of the paper, and of course I have my own two cents to add. I'll discuss that next time.