Activity
Bones lose mineral content when not subjected to loads. Primitive Eskimos led vigorous lives of hunting, kayaking, walking through snow, carrying loads of food, fuel, or children, so it seems unlikely that inactivity caused bone losses found in precontact Eskimos.
Eskimos compared to Pueblos had more evidence of bone demineralization activity. It seems unlikely that the Pueblo life in the high desert had higher bone loads than Eskimos. Walking through the desert is less strenuous than walking in snow with snow shoes and heavy clothing, carrying loads of meat probably is more strenuous than picking corn cobs.
In the 1970s, modern Eskimos getting about 50% of subsistence from hunted wild foods had more demineralization than modern Wisconsin whites who got most if not all of their foods by driving automobiles to supermarkets. Very unlikely that the whites had higher intensity activity overall.
Vitamins
Vitamin A – Modern population data indicates that excessive vitamin A intake relative to vitamin D and K levels may promote osteoporosis. Eskimos who ate animal livers frequently, particularly liver from species high on the food chain (e.g. polar bears), may have ingested levels of vitamin A that would promote osteoporosis.
Vitamin D – Eskimos had extensive summer sun exposure with sufficient skin exposure to generate some vitamin D. Those that ate marine animals would also have gotten large doses of vitamin D from fish and sea mammals. Weston Price reported Eskimos getting at least 10 times the vitamin D found in modern diets. Lack of vitamin D would have caused rickets and poor craniofacial development, neither of which appear to have occurred in either precontact Eskimos or those Weston Price found still eating native diets. The Wainwright Eskimos studied by Mazess got about 50% of their energy from wild foods including fish supplying vitamin D, whereas the whites having higher bone mineral content ate none of those foods. Vitamin D deficiency seems an unlikely cause of Eskimo age-related bone loss.
Vitamin K – Inadequate vitamin K, particularly K2, results in loss of bone matrix. Eskimos who ate ruminant animal fats and livers from caribou would very likely have gotten adequate vitamin K2. This would seem confirmed by the excellent craniofacial development of Eskimos studied by Weston Price, since lack of vitamin K2 would have resulted in poor craniofacial development.
Vitamin B-12 – Deficiency of vitamin B-12 in pregnancy and childhood appears to impair bone mineralization in youth. Eskimos ate plenty of meat and fish rich in vitamin B-12.
Vitamin C – Deficiency of vitamin C would impair formation and repair of the cartilage bone matrix. Eskimos apparently did not suffer from vitamin C deficiency severe enough to impair bone growth during development since most reports including Weston Price have found Eskimos have normal bone growth and development in youth. However, their vitamin C intake fell far short of the 400-500 mg estimated daily intake of an equatorial hunter-gatherer, which is only a fraction of the the intake a comparably sized non-human primate would consume from a wild diet. I consider it possible that their vitamin C intake was suboptimal for maintaining bone matrix during aging.
Mineral Intake
Boron – Modern studies have found higher resistance associated with lower risk of osteoporotic bone fractures among people consuming higher amounts of boron. Fruits, vegetables, and nuts provide most of the boron in modern diets. I have not yet found information of the boron content of fish and meat, the main mineral sources in the Eskimo diet.
Calcium – Eskimos consumed calcium in meat and bones, primarily fish bones. They had an estimated variable intake ranging from 500 mg to 2000 mg daily. Since in most studies including the reports of Weston Price it appears that they developed and maintained normal bones and bone density comparable to non-Eskimos up to the third decade of life, it does not seem likely that calcium deficiency caused their early onset osteoporosis.
Copper – Copper supports collagen formation for bone structure and deficiency results in decreased bone formation and bone deformities, and increases loss of calcium from bone. In the Eskimo diet, meat, particularly organ meats, would have supplied copper. Since Price found isolated Eskimos had no bone deformities, precontact Eskimos probably had adequate copper intake for development.
Magnesium – The bones contain 60 percent of the magnesium in the body. Rude et al found that dietary magnesium deficiency induces bone loss, decrease in osteoblasts, and an increase in osteoclasts in rats maintained at levels of 10%, 25%, and 50% of recommended intakes. They also found that magnesium restriction in humans induces changes that would promote osteoporosis. Of foods eaten by Eskimos, meat does not supply much magnesium but seafoods and kelp do. Nuts and green leafy vegetables supply high amounts.
Manganese – Manganese plays a role in collagen formation and is required for normal bone formation and development.
Phosphorus – Calcium phosphate forms the primary component of bones and teeth. Phosphate deficiency would result in failure to form normal bones. Humans rarely experience phosphorus deficiency, and since meat and fish supply plenty of phosphorus, Eskimos would not have experienced phosphate deficiency unless during starvation.
On the other hand, studies on humans consuming diets with a low calcium:phosphorus ratio produce elevations of parathyroid hormone and urinary calcium (see for example Kemi et al or Calvo).
An Eskimo Analogue Diet
To get some idea of the nutrient profile of a precontact Eskimo diet, I created an Eskimo analogue diet and subjected it to nutrition analysis. I composed it of sardines with edible bones, venison (as an alternative to caribou, not in the database), kelp (8 ounces) and animal fat. About 50% of the protein comes from the sardines, and the rest from venison. The diet supplies 3000 kcal, with 21% of calories from protein and 77% from fat, approximately the ratio recommended by Stefansson.
This slide displays the macronutrient values and ratio of this food selection:
This slide gives the micronutrient analysis in tabular form:
And this slide gives the micronutrient analysis in graphic form:
Using this selection of foods, this diet has adequate calcium but shows significant deficiencies of vitamin A, vitamin C, manganese, potassium, and thiamin. I know that the Eskimos met their vitamin A needs by eating liver regularly. They obtained vitamin C from adrenal glands, and the need for vitamin C is probably reduced by low carbohydrate intake. The manganese content only 36% of recommended levels. As noted above, this deficiencies could have an adverse effect on bones.
Absent the kelp, this diet provides only 16% of the recommended intake of manganese. This means that increased kelp consumption would provide the most efficient way to increase manganese intake without increasing protein intake. Since one-half pound of kelp provides 20% of the daily requirement for manganese, to reach 80% of the recommended level would require adding more than one pound of kelp to the diet, for a total of more than 1.5 pounds of kelp daily. That seems possible and would also increase intake of other minerals including calcium. It would fit with the mineral intake of Eskimos reported by Weston Price.
Including the half-pound of kelp, the diet also provides early 1500 mg of calcium and about 2100 mg of phosphorus. Assuming precontact Eskimos ate like this, the diet does not have a low calcium to phosphorus ratio, so this would probably exclude a low calcium:phosphorus ratio in the precontact Eskimo diet as a factor to their bone condition.
Summary
Thus it seems unlikely to me that isolated coastal Eskimos who ate kelp suffered from any activity or mineral deficiency that could account for their unusual bone metabolism and mineral loss with age. Inland Eskimos who ate less fish and kelp may have had a more difficult time getting adequate calcium and magnesium, since without the kelp this diet would have only 42% of the recommended level of magnesium and about 400 mg less calcium, and without the sardines the calcium intake would fall very low.
It does seem possible that excessive vitamin A could have played a role, at least in some cases where people consumed liver from certain species. Subacute deficiency of vitamin C may also have played a role. On page 72 of NPD, Dr. Price summarized the omnivorous Eskimo diet: "Eskimos were able to provide their bodies with all the mineral and vitamin requirements from sea foods, stored greens and berries and plants from the sea." I don't know what other greens or berries the Eskimos ate, but they would have increased the vitamin C content as well. Thus, I do not feel certain that either of these can completely account for the degree of bone mineral loss observed in Eskimos.
I do want to emphasize the importance of kelp in this menu. If you take it out of the outlined diet, this makes the diet deficient in vitamin E, magnesium, manganese, potassium, and thiamin. It appears that by Weston Price's report, high nutrient density plant foods (seaweeds, greens, and berries) played an important nutritive role in the Eskimo diet.
Addendum 3/13/2010:
Shortly after I posted this I noticed that I did not feel confident in my supposition that Eskimos ate the amount of kelp I proposed in my analogue diet, but I did not have time to edit it. This reminded me that when I posted on the Masai Use of Herbs, in response to a comment I stated that I would post on plant foods used by Eskimos. Then I received comments from Stephan and Tom (below) that expressed the same doubt. I got ahold of two old reports on plants used as food by Eskimos, and from these two papers it appears that coastal Eskimos did not use kelp in anywhere near the quantity I thought possible. It appears that they actually used more of land plants than seaweeds.
So in my next post on this subject I will present a revised Eskimo analogue diet. Suffice it to say the without kelp, the Eskimo diet has multiple mineral deficiencies that could promote osteoporosis.
No comments:
Post a Comment