Aging, bone loss, and the body mass index in Arizona retirees

In order to identify relationships between changes in the body mass index (BMI) and those occurring in bone density with age, data from a sample of 2,075 Arizona retirees aged 60-90 years were compared by age and sex. Remodeling of the diaphysis of the radius follows a pattern that results in an increased diameter of the cortex and medullary cavity in both sexes. However, the resultant decrease in percentage cortical area (PCA) was greater in women than in men. The positive relationship between BMI and PCA is more pronounced in women, who begin to lose bone density earlier than men, and also lose it more rapidly. Despite the fact that average age at menopause is about 50 years and it is generally believed that bone loss slows within 5-10 years after menopause, average PCA values decline from 44% in 60-70 year old women to 37% in 80-90 year old Sun City women and to 36% in Tucson women. The decline in average PCA ranges from 45% in Sun City men and 46% in Tucson for 60-70 year old men to 43% and 42%, respectively, in 80-90 year olds. When the PCA values of women in four BMI categories are compared, cortical area increases with BMI, while medullary cavity values are similar across BMI categories. This relationship between BMI and PCA is much weaker in men. This pattern suggests more vigorous subperiosteal apposition in women with higher BMIs. Endosteal resorption does not seem to be as much affected by the BMI. An additional observation is that the BMIs of Sun City women are lower than those of Tucson women, although the decline in average values with age is very similar in the two populations, with a sharper decline from the 70-80 year group to the 80-90 year group than seen between the 60-70 year group and the 70-80 year group. Average BMIs of males are consistently higher than those of females in all age groups in the Sun City sample, but means for the sexes are very similar in the Tucsonans beyond 70 years. Sun City males of more advanced age are heavier than Tucson males, but the situation is reversed when women are similarly compared. © 1994 Wiley-Liss, Inc.