Arnaud C D, Sanchez S D
Department of Medicine, School of Medicine, University of California, San Francisco 94143.
Annu Rev Nutr. 1990;10:397-414. doi: 10.1146/annurev.nu.10.070190.002145.
Calcium requirements may vary throughout the lifespan. During the growth years and up to age 25-30, it is important to maximize dietary intake of calcium to maintain positive calcium balance and achieve peak bone mass, thereby possibly decreasing the risk of fracture when bone is subsequently lost. The RDA for age 10-25 is 1200 mg/day. Calcium intake need not be greater than 800 mg/day during the relatively short period of time between the end of bone building and the onset of bone loss (30 to 40 years old). Starting at age 40-45, both men and women lose bone slowly, but women lose bone more rapidly around the menopause and for about 10 years after. Intestinal calcium absorption and the ability to adapt to low calcium diets are impaired in many postmenopausal women and elderly persons owing to a suspected functional or absolute decrease in the ability of the kidney to produce 1,25(OH)2D3. The bones then become more and more a source of calcium to maintain critical extracellular fluid calcium levels. Available evidence suggests that the impairments of intestinal calcium absorption observed during the menopause and aging can be overcome only by inordinately large calcium intakes (1500 to 2500 mg/day). Since this amount is difficult to derive from the diet, can cause constipation, and may not prevent trabecular bone loss, it should not be used as a substitute for sex hormone replacement. Women taking estrogen replacement should be provided the RDA for calcium of 800 mg/day at a minimum. Those who cannot or will not take estrogen should be asked to ingest at least 1000 to 1500 mg/day of calcium to delay cortical bone loss and prevent secondary hyperparathyroidism. It should be emphasized that up to 2000 mg/day of calcium is safe in teenaged children and adults. Excessive dietary intake of protein and fiber may induce significant negative calcium balance and thus increase dietary calcium requirements. It is also possible that excessive intakes of phosphate could have a deleterious effect on calcium balance in populations whose need for calcium is great (e.g. growing children) or whose ability to produce 1,25(OH)2D3 is impaired (e.g. the elderly). Moderation in the intake of these nutrients is urged. Generally, the strongest risk factors for osteoporosis are uncontrollable (e.g. sex, age, and race) or less controllable (e.g. disease and medications). However, several factors such as diet, physical activity, cigarette smoking, and alcohol use are lifestyle related and can be modified to help reduce the risk of osteoporosis.
钙的需求量在整个生命周期中可能会有所不同。在生长阶段以及直至25 - 30岁，最大化饮食中钙的摄入量以维持钙的正平衡并达到峰值骨量非常重要，从而可能降低随后骨质流失时骨折的风险。10 - 25岁的推荐膳食摄入量（RDA）为每日1200毫克。在骨骼生长结束至骨质流失开始的相对较短时期（30至40岁）内，钙的摄入量不必超过每日800毫克。从40 - 45岁开始，男性和女性都会缓慢地骨质流失，但女性在绝经前后以及绝经后的大约10年中骨质流失更为迅速。由于怀疑肾脏产生1,25(OH)₂D₃的能力出现功能性或绝对性下降，许多绝经后女性和老年人肠道钙吸收以及适应低钙饮食的能力会受损。于是骨骼越来越成为维持细胞外液关键钙水平的钙源。现有证据表明，在绝经和衰老过程中观察到的肠道钙吸收受损情况，只有通过摄入极高量的钙（每日1500至2500毫克）才能克服。由于这个量很难从饮食中获取，可能导致便秘，并且可能无法预防小梁骨丢失，所以它不应被用作性激素替代疗法的替代品。接受雌激素替代疗法的女性，钙的RDA至少应为每日800毫克。那些不能或不愿服用雌激素的女性应被要求摄入至少每日1000至1500毫克的钙，以延缓皮质骨丢失并预防继发性甲状旁腺功能亢进。应当强调的是，青少年和成年人每日摄入高达2000毫克的钙是安全的。饮食中蛋白质和纤维的过量摄入可能会导致显著的钙负平衡，从而增加饮食中钙的需求量。对于钙需求较大的人群（如成长中的儿童）或肾脏产生1,25(OH)₂D₃能力受损的人群（如老年人），过量摄入磷酸盐也可能对钙平衡产生有害影响。因此，建议适度摄入这些营养素。一般来说，骨质疏松症最强的风险因素是无法控制的（如性别、年龄和种族）或较难控制的（如疾病和药物）。然而，饮食、体育活动、吸烟和饮酒等几个因素与生活方式有关，可以通过改变这些因素来帮助降低患骨质疏松症的风险。
