Advances in Nutritional Research最新文献

Hip fracture incidence seems to be lower in Japan than in many Western countries, but the difference is apparently becoming smaller with progressive Westernization of the Japanese lifestyle and nutritional habits. Nutrition cannot explain the lower incidence of hip fracture. A lower calcium intake prevails in Japan. Genetic differences in body build, including a lower center of gravity, better motor function and agility, well developed hip musculature and small but more fracture-resistant bones secondary to a difference in life- and work-style may contribute to fewer falls and a lower fracture rate among Japanese than among their Western counterparts. Such traditional lifestyle habits as sitting directly on the floor are rapidly decreasing, and time will tell how much of the low incidence of hip fracture in Japan can be explained by lifestyle and how much by genetic and other factors. The Japanese women who now enjoy a low hip fracture incidence led a hard physical life when they were young. This may be a lesson to the young of future generations in how to avoid bone fractures when they are old. Bone health may be achieved by enjoying life through sports or even the tea ceremony in place of the hard physical work of their ancestors, which is gradually disappearing.

A plethora of investigations in recent years has demonstrated the occurrence of ethnic differences in bone mineral content, bone density and fracture rates. These findings indicate that genetic determinants exist both for bone development during growth and for bone loss during aging. Twin and parent-offspring studies have corroborated the existence of a hereditary component. It is most evident in the greater bone mass and lower fracture rate in blacks than in whites. Differences in bone mass between Asians and whites are less clear than between blacks and whites because of disparities in body size and other confounding factors. Black children and adults excrete less urinary calcium than whites on essentially the same diets and consequently retain more calcium in their skeletons. Better calcium retention is commensurate with the faster rate of bone growth of black children.

Survey data confirm that the dietary pattern of many American women who are at high risk of developing osteoporosis is typically high in phosphorus and low in calcium. The imbalance between calcium and phosphorus intake may become more pronounced with continued changes in food preferences and the growing use of phosphorus-containing food additives. Recent studies in young women have shown that a high phosphorus diet moderately low in calcium results in a mild secondary hyperparathyroidism that persists over 4 weeks. Plasma levels of calcitriol did not change despite changes in PTH and serum ionized calcium. Studies on men have shown that dietary phosphorus at levels within the normal range of intakes can affect the renal production and serum concentration of calcitriol. High phosphorus intakes for ten days reduced their plasma calcitriol levels; a 70% reduction in phosphate intake significantly increased their plasma calcitriol. Thus, several lines of evidence indicate that prolonged high phosphorus intake may impair the usual homeostatic mechanisms that come into play when dietary calcium is limited. This, in turn, could impair achievement of maximal bone mass or accelerate bone loss. Although no clinical studies have linked high phosphorus intake with lower bone mass or higher rates of bone loss in humans, this relationship has been demonstrated in animal models. For example, young beagles fed high phosphorus, moderately low calcium diets showed a significant reduction in vertebral bone mass. Current dietary patterns of high phosphorus, low calcium consumption result in persistent changes in calcium regulating hormones that are not conducive to maximizing peak bone mass during growth or slowing the rate of aging bone loss. The net effect of the present dietary pattern on bone status, particularly in teenage and young adult women, needs to be determined. Optimal nutrition early in life, which may include higher calcium and lower phosphorus intakes, together with adequate exercise, may be the most cost-effective approach to the prevention of osteoporotic fractures.

There are many data indicating that osteoporotic fractures, and particularly hip fractures, are less frequent in obese subjects. Overweight and obese women have a higher bone mass after menopause than women of the same age who are not overweight, and thus in all probability have a slower bone loss. This protective effect appears to be related both to mechanical factors and to estrogen synthesis in adipose tissue.