Bone mineral content in St. Lawrence Island Eskimos.

Abstract

Bone mineral content (BMC) of the radius was determined for 117 male and 124 female St. Lawrence Island Eskimos volunteers using a Norland-Cameron bone mineral analyzer with an 125I source. Results of this study support earlier findings showing low BMC in northern Eskimos compared to Wisconsin Whites. In particular, Eskimos lose bone starting at earlier ages and at a greater rate than other populations. For St. Lawrence Island males over age 50, the change in BMC of the radius is -5.8% per decade compared with an average loss of 4.0% per decade in Wisconsin White samples. The rate of BMC decrease in Eskimo females older than age 45 is much greater than in males. The average diminution per decade is 13.9% contrasted to a -10.0% per decade loss in Wisconsin White females. Compared to north Alaska Inupiaq Eskimos, St. Lawrence Island Yupik Eskimos display a remarkably similar pattern of age-related bone loss. This pattern, indigenous to all Eskimos, of rapid loss with age is manifest in both preand post-contact Eskimo skeletons throughout the Arctic. Measurements of bone mineral content (BMC) in vivo using direct photon absorptiometry have been widely accepted in clinical studies of bone (Mazess, 1979), but have not been widely used for assessing population differences (Mazess and Christiansen, 1982; Mazess, 1980). The earlier studies of Trotter (1956), Baker and Newman (1957), Lowrance and Latimer (1957), Mazess (1966), and others demonstrated that the weight and density of the long bones varies considerably among populations. These studies were, by necessity, in vitro, and consequently limited to archaeological or cadaveral series. The use of non-invasive methods has made it feasible to study population variation in bone (Garn, 1970) in populations of considerable anthropological interest. However, the cortical thickness measurements in common use for population assessment do not reflect intracortical porosity which is a significant parameter in aging bone changes and in osteoporosis (Dickenson et al. 1981). We report here on the BMC in Yupik-speaking Eskimos of St. Lawrence Island. Mazess (1971) first noted the reduced bone mass and lower skeletal weight of the extinct Sadlermiut Eskimo from Southampton Island in north central Canada. Later observations showed living Eskimos from north Alaska and from western Canada also had a low BMC combined 1 Laboratory of Biological Anthropology, Department of Biobehavioral Sciences, University of Connecticut, Storrs, CT 06268. 2Department of Medical Physics, University of Wisconsin Medical School, Madison, Wisconsin 53706. Human Biology, February 1984, Vol. 56, No. 1, pp. 63-77. © Wayne State University Press, 1984 This content downloaded from 157.55.39.107 on Wed, 30 Mar 2016 05:19:32 UTC All use subject to http://about.jstor.org/terms 64 А. В. Harper , W. S. Laughlin, and R. B. Mazess with early and rapid onset of osteoporosis (Mazess and Mather, 1974, 1975). It was suggested that the bone deficiency apparent in the high Arctic Inupiaq Eskimo was related to the high protein, high phosphate, low calcium sea mammal diet. From earlier studies (Merbs, 1969) it was patently clear that the northern Inupiaq Eskimo had a high frequency of osteoporosis which started at early ages. It was also clear that the Northern Eskimo had low bone mass and density for several hundred years prior to western contact. The nature of bone loss with age in southern (Yupik-speaking) Eskimos was until recently unknown. Studies based upon skeletonized ancestral-antecedent populations of Aleuts, Yupik Eskimos, and Inupiaq Eskimos have revealed a major cline in bone cortical thickness (Laughlin et al. 1979; Thompson and Gunness-Hey, 1981). Cortical thickness is highest in the ancestral Umnak-Kodiak homeland of the Bering Sea Mongoloids and decreases in populations north along the Alaskan coast to the Arctic Circle, the approximate demarcation point between Yupik and Inupiaq Eskimo. Cortical thickness values diminish even more in the Inupiaq Eskimos extending east across north Alaska, Canada and Greenland. The difference between the terminal isolates, Aleuts and Greenland Inupiaq Eskimos, are as great as the difference in cortical thickness between male and female in the same isolate. Similarly, femoral BMC measured by direct photon absorptiometry mirrors the highly significant differences between Aleuts, on one hand and northern Eskimos on the other (Laughlin et al. 1979; Frank, 1980; Gunness-Hey, 1980; Thompson et al. 1981). By way of brief background on the evolutionary relationship among the Bering Sea Mongoloids, we should note that these populations, Yupik Eskimos and Inupiaq Eskimos, were once resident populations on the former Bering Land Bridge. Approximately 9,000 BP the Aleuts and Eskimos diverged, Aleuts moving into the Aleutian Islands and Eskimos occupying the coast of southern Alaska. About 5,000 BP the Eskimo had established permanent colonies on the Seward Peninsula and split into Yupik speaking southern Eskimo and Inupiaq speaking northern Eskimo. The northern Inupiaq made at least three unsuccessful attempts to establish colonies on Greenland (Harper, 1980).