622 PART 4 Nutrition for Health and Fitness

TABLE 24-3

Recommended Intakes of Bone-RelatedNutrients for Adults

Per Day

nificant increases in spinal and total body BMD. A few studies have followed up the subjects who gained BMD on earlier supplementation, but without further supplements of calcium the mean BMD values of the treated groups re- verted back to the mean values of the control groups. These reports suggest that the higher intakes need to be consumed

Calcium

Vitamin D Magnesium Manganese ZincBoronCopperVitamin K

1500 mg/day for postmenopausalwomen, 1000-1200 for younger women

600-1000 units400-600 mg2-5 mg15 mg3 mg2-3 mg500 mcg

consistently to maintain any gains in BMD from calciumsupplements alone. Thus the question still remains of whether a brief l-year gain in BMD resulting from a cal- cium supplement during early life (i.e., teenage years) may translate into later protection against osteoporosis. But it seems more likely that keeping the gains in BMD accrued before age 20 may best be met by a combination of regular physical activity and a reasonable consistent daily calcium intake that approaches the current AI.

Calcium Bioavailability

Calcium bioavailability from foods is generally similar tohave been hypothesized to improve bone mass and density in postmenopausal women and older men, but most inves- tigations of these dietary components have not supported the hypothesis.

Recommendations for the intakes of calcium and severalbone-related nutrients by adults are shown in Table 24-3.

Calcium Intake

Calcium from FoodsCalcium intake in the primary prevention of osteoporosis has received much attention. The Institute of Medicine recommendations for calcium, vitamin D, and a few other nutrients are given as adequate intakes (AIs), because only the mean requirements for calcium and vitamin D during the stages of the life cycle could be quantified. The AI for calcium from preadolescence (age 11 years) through adoles- cence (up to 19 years) was increased to 1300 mg/day in the latest report. AIs for calcium are the same for each gender across the life cycle (see the dietary recommended intakes on inside front cover).

Calcium intakes typically do not meet the recommendedAI for all ages beyond 11 years, especially females. Accord- ing to NHANES data (NHANES, 2007), teen and adult women consume considerably less than the current AIs. Men are more likely to consume somewhat greater amounts than females, but they also do not meet the recommended levels after 50 years of age. These deficits translate, on aver- age, into the need for roughly an additional 500 mg/day for teenage females and adult women.

Food sources are recommended first for supplying cal-cium needs because of the coingestion of other essential nutrients. Reaching AI levels of calcium from foods should be the first goal, but if insufficient amounts of calcium from foods are consumed, supplements of calcium should then be ingested to reach the age-specific AI.

Calcium from SupplementsNumerous studies of calcium supplementation in all age- groups and especially in females have typically shown sig-

that of supplements. Calcium bioavailability from supple- ments containing various anion combinations is very good; however, a few preparations that contain citrate as the anion may have a slightly higher bioavailability.

Calcium bioavailability from foods is generally good, but from a few foods such as spinach it may be low and adversely affect calcium nutrition status. Wheat bread may be a good source of calcium for those who consume several servings of bread a day; green leafy vegetables such as broccoli, kale, and bok choy also have good bioavailability; and calcium from soybeans is very well absorbed. However, spinach and a few other high oxalate-containing vegetables have low calcium bioavailability. The consumption of dairy products, especially high-calcium milks, cheeses, and yogurts, appears to be the best way for most individuals to meet their daily calcium requirements. However, it is not the only way; non- dairy sources of calcium such as almonds, tofu, calcium- fortified nondairy milks and juices, and dark-green leafy vegetables are excellent options.

Additional benefits of meeting calcium requirements from foods alone are that the foods containing calcium are also rich in several other nutrients needed for health in gen- eral, and for bone health in particular, and that the con- sumption of a calcium-rich diet from foods is also a marker of a balanced intake with respect to practically all micronu- trients. The amount of calcium in major food sources is listed in Table 24-4.

Calcium Bioavailability fromCalcium SupplementsCalcium bioavailability from calcium supplements depends on the anion used, but practically all calcium-containing supplements currently on the market have good bioavail- ability. Calcium citrate malate supplements appear to be absorbed slightly more efficiently than calcium carbonate and other calcium supplements, but the difference is typi- cally only a couple of percentage points. Calcium carbonate can have a constipating effect that may be minimized by dividing the dose and taking more fluids and fiber. High- dose calcium supplements may reduce the absorption of