Monday, April 18, 2011

Low bone mineral content in older Eskimos: Meat-eating or shrinking?

Mazess & Mather (1974) is probably the most widely cited article summarizing evidence that bone mineral content in older North Alaskan Eskimos was lower (10 to 15 percent) than that of United States whites. Their finding has been widely attributed to the diet of the Eskimos, which is very high in animal protein. Here is what they say:

“The sample consisted of 217 children, 89 adults, and 107 elderly (over 50 years). Eskimo children had a lower bone mineral content than United States whites by 5 to 10% but this was consistent with their smaller body and bone size. Young Eskimo adults (20 to 39 years) of both sexes were similar to whites, but after age 40 the Eskimos of both sexes had a deficit of from 10 to 15% relative to white standards.”

Note that their findings refer strictly to Eskimos older than 40, not Eskimo children or even young adults. If a diet very high in animal protein were to cause significant bone loss, one would expect that diet to cause significant bone loss in children and young adults as well. Not only in those older than 40.

So what may be the actual reason behind this reduced bone mineral content in older Eskimos?

Let me make a small digression here. If you want to meet quite a few anthropologists who are conducting, or have conducted, field research with isolated or semi-isolated hunter-gatherers, you should consider attending the annual Human Behavior and Evolution Society (HBES) conference. I have attended this conference in the past, several times, as a presenter. That gave me the opportunity to listen to some very interesting presentations and poster sessions, and talk with many anthropologists.

Often anthropologists will tell you that, as hunter-gatherers age, they sort of “shrink”. They lose lean body mass, frequently to the point of becoming quite frail in as early as their 60s and 70s. They tend to gain body fat, but not to the point of becoming obese, with that fat replacing lean body mass yet not forming major visceral deposits. Degenerative diseases are not a big problem when you “shrink” in this way; bigger problems are  accidents (e.g., falls) and opportunistic infections. Often older hunter-gatherers have low blood pressure, no sign of diabetes or cancer, and no heart disease. Still, they frequently die younger than one would expect in the absence of degenerative diseases.

A problem normally faced by older hunter-gatherers is poor nutrition, which is both partially caused and compounded by lack of exercise. Hunter-gatherers usually perceive the Western idea of exercise as plain stupidity. If older hunter-gatherers can get youngsters in their prime to do physically demanding work for them, they typically will not do it themselves. Appetite seems to be negatively affected, leading to poor nutrition; dehydration often is a problem as well.

Now, we know from this post that animal protein consumption does not lead to bone loss. In fact, it seems to increase bone mineral content. But there is something that decreases bone mineral content, as well as muscle mass, like nothing else – lack of physical activity. And there is something that increases bone mineral content, as well as muscle mass, in a significant way – vigorous weight-bearing exercise.

Take a look at the figure below, which I already discussed on a previous post. It shows a clear pattern of benign ventricular hypertrophy in Eskimos aged 30-39. That goes down dramatically after age 40. Remember what Mazess & Mather (1974) said in their article: “… after age 40 the Eskimos of both sexes had a deficit of from 10 to 15% relative to white standards”.


Benign ventricular hypertrophy is also known as athlete's heart, because it is common among athletes, and caused by vigorous physical activity. A prevalence of ventricular hypertrophy at a relatively young age, and declining with age, would suggest benign hypertrophy. The opposite would suggest pathological hypertrophy, which is normally induced by obesity and chronic hypertension.

So there you have it. The reason older Eskimos were found to have lower bone mineral content after 40 is likely not due to their diet.  It is likely due to the same reasons why they "shrink", and also in part because they "shrink". Not only does physical activity decrease dramatically as Eskimos age, but so does lean body mass.

Obese Westerners tend to have higher bone density on average, because they frequently have to carry their own excess body weight around, which can be seen as a form of weight-bearing exercise. They pay the price by having a higher incidence of degenerative diseases, which probably end up killing them earlier, on average, than osteoporosis complications.

Reference

Mazess R.B., & Mather, W.W. (1974). Bone mineral content of North Alaskan Eskimos. American Journal of Clinical Nutrition, 27(9), 916-925.

20 comments:

justdoinglife said...

Thank you for your column.

1974. My first work in the Canadian north was 1971. By that time, our Canadian natives were mainly living in settlements, and had been doing so for 20 years. The research was being done on the "town natives", at the medical facility ( skid trailers) adjacent to the new "medical center" we were building.

The town natives ate from the Bay store, while the country natives were seldom seen. What population was being studied, and how were they living? redundant question.

Ned Kock said...

My take is that both studies, by Mazess & Mather and Kjærgaard et al., involved semi-Westernized Eskimos. The post on the Kjærgaard et al. study is the one linked above the graph. If you take a look at it, you’ll see that the heart disease markers are consistent with them being mostly on their traditional diet. Fully Westernized Eskimos tend to show clear signs of degenerative diseases.

Chuck said...

the study measures the mineral content of the forearm (radius). would this indicate whether someone worked with there hands a lot because that is the load bearing i would expect in this area of the body. my question would be regardless of weight, did white americans studied of that time period work with their hands more than the age matched eskimo population. i am not sure of the answer but i would speculate even at 40+, the eskimos still were doing as much with their hands as the white americans. or maybe i am wrong. i don't think the exercise craze really was prevelant in the early 70's.

Anonymous said...

Hi Ned,

Great information, please keep correlating and drawing conclusions, this is very practical for people that can't dig much on the reasech for different reasons.

I happen to be a student of one professor you know, Dr. Oscar Flores. He's giving classes in Monterrey, Mexico, in my Master's degree in IT. Because I'm interested in health, one day I showed him you blog and to my surprise he knew you, personally.

Keep up the great work.

Regards,

--Enrique C.

Dana Seilhan said...

That last paragraph is kind of muddled, sounds like Americans suffer from more degenerative diseases because they exercise more?

Just got done, over the weekend, reading that NYT article about a supposed link between obesity and how much one moves around fidgeting and doing everyday tasks. The implication was that fat people deliberately chose not to be fidgety or move around a lot, and because they weren't burning those calories, they packed 'em on as fat. Clearly the researcher had not read any of the research that Gary Taubes outlined, to wit: those inclined to become obese are conserving energy in fat tissue rather than releasing it between meals and, as a result, lean tissue is not getting enough energy and slows down its activity as a result.

Blogger is acting up, maybe my comment's too long so I'll make this a two-parter...

Dana Seilhan said...

part 2... sheesh...



The degenerative diseases in Americans have to do with our poor diet, and they strike anyone regardless of weight. We notice them more in obese people because we have already made up our minds that fat people are ill. If you look around and listen, though, there are lots of anecdotal accounts of slender people getting heart disease and type 2 diabetes and cancer and hypertension and so on as well, though. They're being overlooked until they're already sick and can't be ignored anymore because "everybody knows" slender people are healthy.

Inuit people eat a good diet, period. The bone mass, not the lack of degenerative diseases, comes from the exercise. The lack of degenerative diseases comes from the diet. While we would probably reduce obesity rates simply by changing the diet because our industrial diet drives the metabolic changes that produce obesity in SOME people... our bone mass ultimately will be preserved by our level of activity. The two are separate matters.

Melissa said...

Old ladies have been "little old ladies" in most societies until now. This 90-100 year old woman from Kitava is a prime example of such shrinking http://www.flickr.com/photos/rietje/4261866127/in/photostream/

Ned Kock said...

Hi Chuck. The measurements were taken in 1968 and 1969; for the humerus, radius and ulna. I’d suspect those measurements would reflect (a) overall bone mineral content, and (b) activities involving lifting heavy things with your hands including your own body (e.g., climbing trees).

Ned Kock said...

Hi Enrique, thanks. Please send my best regards to Oscar.

Ned Kock said...

Hi Dana. Obesity is a MAJOR risk factor for most degenerative diseases.

Ned Kock said...

Thanks for the link Melissa.

Greg said...

Do we have any idea of the relative calorie consumption? More calories could signal growth (or less shrinkage) to the metabolism.

Perhaps Americans consume more calories in older age than their Inuit peers because they don't have to ask someone else to hunt for them.

Just a guess- would be nice to have it shot down by some evidence

Ned Kock said...

Hi Greg. I don’t think caloric intake is reported in the article.

It is pretty well established that overweight folks tend to have some protection against osteoporosis, but risk of degenerative diseases goes up with body fat gain. So if one is overweight due to body fat gain, it is not good news.

The ideal scenario is keeping a low body fat as one gets older, while retaining as much as lean body mass as possible. It can be done, as we can see from people like Art De Vany (in his 70s) and Mark Sisson (in his 50s). Eating a balanced diet of natural foods and doing weight training as one gets older helps.

Ned Kock said...

When I say “keeping a low body fat” I don’t mean that everybody should be shredded, down to single digits. I think that different people have different optimal levels of body fat for them: http://bit.ly/g97Fk8.

Jack C said...

Ned,

The lower bone density of elderly Eskimos compared to elderly whites may be due in part to the higher fat intake of the Eskimos.

The presence of undigested food at the ileum results in inhibition of movement of food through the small intestine resulting in greater absorption of nutrients, a phenomenon called the "ileum brake". The most potent trigger of the ileum brake is fat. The ileum brake is mediated largely by cholecystokinin, an appetite suppressing hormone that is secreted by the gut in a dose dependent manner in response to the presence of fat and which results in appetite suppression and reduced food intake.

Aging results in an increase in secretion of CCK as well as an increase in sensitivity to CCK, often resulting in excessive weight loss.

Since the diet of Eskimos is higher in fat than the diet of whites, it stands to reason that they would experience a greater degree of appetite suppression with age that would result in nutrient deficiencies that could lead to increased osteoporosis.

allison said...

In typical primitive societies, particularly as noted among American Indian tribes in the 1800s, old people tend to be venerated by society and are not required to hunt, work or fight. That would help explain increased rates of atrophy and osteoporosis.

Ned Kock said...

Hi Jack. I had a feeling you’d say that. Good point.

Ned Kock said...

Hi Allison. Thanks for stopping by and commenting.

I guess the aboriginal in the middle on the photo on this post didn’t get much respect from his peers: http://bit.ly/el1ruw.

If yes, I guess that it might have been good for him.

David Isaak said...

"...elderly (over 50 years)..."

Yanno what I say? I say, hey--take an effing hike!

"Elderly" indeed. Remind me of that (with the memory loss and all) whe n it's time to piss on the graves of these researchers.

If 50 is elderly, why don't I qualify for Medicare? Or even senior discounts at the movies?

My bones are denser than ever. My cranium is, too.

Ned Kock said...

Hi David. I had the same reaction, and wondered if the definition of elderly was in any way related to the article having been published in the 1970s.