Malocclusion: Disease of Civilization

In his epic work Nutrition and Physical Degeneration, Dr. Weston Price documented the abnormal dental development and susceptibility to tooth decay that accompanied the adoption of modern foods in a number of different cultures throughout the world. Although he quantified changes in cavity prevalence (sometimes finding increases as large as 1,000-fold), all we have are Price's anecdotes describing the crooked teeth, narrow arches and "dished" faces these cultures developed as they modernized.

Price published the first edition of his book in 1939. Fortunately, Nutrition and Physical Degeneration wasn't the last word on the matter. Anthropologists and archaeologists have been extending Price's findings throughout the 20th century. My favorite is Dr. Robert S. Corruccini, currently a professor of anthropology at Southern Illinois University. He published a landmark paper in 1984 titled "An Epidemiologic Transition in Dental Occlusion in World Populations" that will be our starting point for a discussion of how diet and lifestyle factors affect the development of the teeth, skull and jaw (Am J. Orthod. 86(5):419)*.

First, some background. The word occlusion refers to the manner in which the top and bottom sets of teeth come together, determined in part by the alignment between the upper jaw (maxilla) and lower jaw (mandible). There are three general categories:

• Class I occlusion: considered "ideal". The bottom incisors (front teeth) fit just behind the top incisors.
• Class II occlusion: "overbite." The bottom incisors are too far behind the top incisors. The mandible may appear small.
  
• Class III occlusion: "underbite." The bottom incisors are beyond the top incisors. The mandible protrudes.
  

Malocclusion means the teeth do not come together in a way that's considered ideal. The term "class I malocclusion" is sometimes used to describe crowded incisors when the jaws are aligning properly.

Over the course of the next several posts, I'll give an overview of the extensive literature showing that hunter-gatherers past and present have excellent occlusion, subsistence agriculturalists generally have good occlusion, and the adoption of modern foodways directly causes the crooked teeth, narrow arches and/or crowded third molars (wisdom teeth) that affect the majority of people in industrialized nations. I believe this process also affects the development of the rest of the skull, including the face and sinuses.

In his 1984 paper, Dr. Corruccini reviewed data from a number of cultures whose occlusion has been studied in detail. Most of these cultures were observed by Dr. Corruccini personally. He compared two sets of cultures: those that adhere to a traditional style of life and those that have adopted industrial foodways. For several of the cultures he studied, he compared it to another that was genetically similar. For example, the older generation of Pima indians vs. the younger generation, and rural vs. urban Punjabis. He also included data from archaeological sites and nonhuman primates. Wild animals, including nonhuman primates, almost invariably show perfect occlusion.

The last graph in the paper is the most telling. He compiled all the occlusion data into a single number called the "treatment priority index" (TPI). This is a number that represents the overall need for orthodontic treatment. A TPI of 4 or greater indicates malocclusion (the cutoff point is subjective and depends somewhat on aesthetic considerations). Here's the graph: Every single urban/industrial culture has an average TPI of greater than 4, while all the non-industrial or less industrial cultures have an average TPI below 4. This means that in industrial cultures, the average person requires orthodontic treatment to achieve good occlusion, whereas most people in more traditionally-living cultures naturally have good occlusion.

The best occlusion was in the New Britain sample, a precontact Melanesian hunter-gatherer group studied from archaeological remains. The next best occlusion was in the Libben and Dickson groups, who were early Native American agriculturalists. The Pima represent the older generation of Native Americans that was raised on a somewhat traditional agricultural diet, vs. the younger generation raised on processed reservation foods. The Chinese samples are immigrants and their descendants in Liverpool. The Punjabis represent urban vs. rural youths in Northern India. The Kentucky samples represent a traditionally-living Appalachian community, older generation vs. processed food-eating offspring. The "early black" and "black youths" samples represent older and younger generations of African-Americans in the Cleveland and St. Louis area. The "white parents/youths" sample represents different generations of American Caucasians.

The point is clear: there's something about industrialization that causes malocclusion. It's not genetic; it's a result of changes in diet and/or lifestyle. A "disease of civilization". I use that phrase loosely, because malocclusion isn't really a disease, and some cultures that qualify as civilizations retain traditional foodways and relatively good teeth. Nevertheless, it's a time-honored phrase that encompasses the wide array of health problems that occur when humans stray too far from their ecological niche. I'm going to let Dr. Corruccini wrap this post up for me:

I assert that these results serve to modify two widespread generalizations: that imperfect occlusion is not necessarily abnormal, and that prevalence of malocclusion is genetically controlled so that preventive therapy in the strict sense is not possible. Cross-cultural data dispel the notion that considerable occlusal variation [malocclusion] is inevitable or normal. Rather, it is an aberrancy of modern urbanized populations. Furthermore, the transition from predominantly good to predominantly bad occlusion repeatedly occurs within one or two generations' time in these (and other) populations, weakening arguments that explain high malocclusion prevalence genetically.

* This paper is worth reading if you get the chance. It should have been a seminal paper in the field of preventive orthodontics, which could have largely replaced conventional orthodontics by now. Dr. Corruccini is the clearest thinker on this subject I've encountered so far.

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Ischemic Heart Attacks: Disease of Civilization

Or, more precisely, disease of Western industrial civilization.

The scientific literature contains examples of cultures that don't suffer from the chronic non-communicable diseases that are so common in modern societies. Much of what I've read indicates that heart attacks are practically unique to cultures that have adopted industrial foodways and a modern lifestyle, being infrequent or entirely absent in those that have not.

I recently came across an incredible paper from 1964 in the American Journal of Cardiology, titled "Geographic Pathology of Myocardial Infarction", by lead author Dr. Kyu Taik Lee (Am. J. Cardiol. 13:30. 1964). This was published during a period of intense research into the cardiovascular health of non-industrial cultures, including Dr. George V. Mann's famous study of the Masai.

The first thing Lee and his colleagues did was collect autopsy statistics from San Francisco and Los Angeles hospitals. They analyzed the data by race, including categories for Caucasian-Americans (white), Japanese-Americans, Chinese-Americans, and Filipino-Americans. All races had a similar incidence of autopsy-proven myocardial infarction (MI = heart attack), including both silent (healed) and fatal MI. For comparison, they included a table with autopsy data from hospitals in Tokyo, South Japan and North Japan. I'm including the data from Tokyo in the graph because it's also an urban environment, but the finding was the same in all three regions. Here's what they found, by age group: The Japanese had a very low rate of MI compared to both Caucasian-Americans and Japanese-Americans. The rate of MI in Caucasian-Americans and Japanese-Americans did not differ significantly. Thus, location but not race determined the susceptibility to MI.

Next, the investigators collected autopsy data from hospitals in New Orleans, again divided by race. This time they exained Caucasian-Americans and African-Americans. Both groups had a very high rate of MI, as expected, although the African-Americans had a lower rate than Caucasian-Americans. They also collected data from autopsies in Nigeria and Uganda for comparison. Here are the data for men: And for women: Again, location but not race largely determined the incidence of MI. MI was extremely rare in the African autopsies. Here's what they had to say:

There was only 1 case of healed myocardial infarction among over 4,000 adult autopsies in the Uganda series, and only 2 cases of healed myocardial infarction among over 500 adult autopsies in the Nigerian series. In the New Orleans Negro series the occurrence rate was far greater in every sex and age group than in either one of the Negro series in East and West Africa.

Over 4,500 autopsies and not a single fatal MI. If this isn't worth studying, what is? These data should be part of first-year training in medicine and health programs.

To satisfy the skeptics, Lee and colleagues imported hundreds of hearts from consecutive autopsies in Albany (USA), Africa, Korea and Japan. They had an American pathologist analyze them side-by side to eliminate any diagnostic bias. Here's what they found:

In the African Negro series no infarct was found in any age group [out of 244 hearts, 39 over 60 years old]. In the Korean series there were only 2 cases of myocardial infarction [out of 106 hearts] and they were both women... In the Japanese series there were 8 cases of myocardial infarction in 259 hearts. All were men...

In the American sample, nearly 40% of the hearts of men and women over 60 showed signs of MI. The findings of the American pathologist confirmed the international autopsy data, showing that diagnostic bias did not contribute to the results significantly. They also took measurements of the thickness of the coronary artery wall, an index of atherosclerosis. They found that the Americans had the most atherosclerosis, but all cultures had some degree of it and there was overlap in the amount of atherosclerosis between samples. This led the investigators to state:

Myocardial infarction and coronary thrombosis are almost nonexistent in Uganda and Nigeria, and the amount of coronary arteriosclerosis is significantly less in Africans than in whites. However, in the two groups there was some overlapping in the degree of arteriosclerosis. No Africans had infarcts, but some had the same or a greater degree of coronary arteriosclerosis as a few whites who had myocardial infarctions. One explanation for this may be that some difference in clotting or clot-lysis mechanisms is present in the two groups. In a previous study, we showed that the incidence of thromboembolic phenomena in the pulmonary circulation [blood clots in the lungs] was low in East Africans as compared with Americans.

Now, the authors' conclusions:

These data strongly suggest that among the Orientals the environmental factor is playing a major role in the etiology of myocardial infarction and coronary thrombosis. If the genetic factor is an important one, those Orientals who moved to this country many years ago or who were born in this country should still maintain their low occurrence rate of myocardial infarction at least to some extent, and one would not expect to see similar occurrence rates of myocardial infarction in Orientals and whites as old as 50 to 59 years... As with the Orientals, this suggests that for Negroes in the United States environmental factors are more important than genetic factors in the etiology of myocardial infarction.

Africans in Africa and Japanese in Japan = low incidence of MI. Africans, Japanese and Caucasians in the US = high and similar incidence of MI. Genes only influence a person's susceptibility to MI when they live in an environment that promotes MI. Otherwise, genes are basically irrelevant.

What do the traditional diets and lifestyles of Japan and Africa have in common? Not much. Even within Nigeria, the diet varies from heavily starch-based (root vegetables, soaked/fermented non-gluten grains, beans, plantains) to mostly reliant on high-fat dairy and meat. In fact, I believe it's the wrong question to ask. A better question is "what do we eat/do in the US that traditional Japanese, Koreans, Chinese, Polynesians, Melanesians and Africans don't"? For starters, none of them rely on industrial vegetable oils, sugar and wheat to nearly the same extent as modern America. Their food is generally prepared at home using wholesome ingredients and traditional methods.

They probably get more exercise than Americans, even if it's only walking in Tokyo or domestic tasks for women in parts of Africa. Traditional Africans surely get more sunlight and thus more vitamin D. I can't imagine life is less stressful in Tokyo than in San Francisco or Los Angeles.

I really like this study, and I think these graphs should be disseminated as much as possible. I've prepared high-resolution versions in JPEG, Powerpoint and PDF formats. E-mail me (click on my profile for the link) if you would like a copy. Let me know which format(s) you want.

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