cil, 1978) should be sufficient to support maintenance of adult nonhuman primates, assuming appropriate P and adequate vitamin D consumption or sufficient ultraviolet B (UVB) exposure. When expressed on a dietary dry matter (DM) basis, this estimated Ca requirement would be 0.55% (assuming 10% moisture in the air-dry diet). Lactation can be expected to increase the demand for Ca, particularly in mothers with more than one offspring, but bone reserves and increased food intake during lactation can compensate to some extent in the short term. With proper diet, at least partial postweaning restoration of bone Ca reserves (depleted by lactation) has been seen in humans (Prentice, 2000).
Although juveniles of the larger primate species grow relatively slowly, compared with the young of many other mammals, the period of growth will probably raise the requirement for both Ca and P over maintenance requirements. Furthermore, the growth of small species, such as marmosets and tamarins, is sufficiently rapid that Ca and P requirements will increase.
Dietary protein and sodium concentrations can influence requirements for Ca. High sodium intakes result in higher sodium concentrations in glomerular filtrate, competing with Ca for renal tubular reabsorption (Nordin et al., 1993). In humans, increased Ca excretion occurs when protein and sodium intakes are high (Heaney and Recker, 1982; Matkovic et al., 1995; Nordin, 1997). The negative Ca balance associated with high protein intakes might be due to increased glomerular filtration and decreased renal Ca reabsorption as end-products of protein metabolism, such as phosphate and possibly sulfate, complex Ca in the renal tubules and carry it out in the urine (Johnson et al., 1970; Spencer et al., 1978; Nordin, 1997). However, Grynpas et al. (1993) found that free-ranging rhesus monkeys from the Caribbean Primate Research Center that had been provisioned with either a 15% or a 25% protein extruded diet for most of their lives were not different in vertebral mineral concentrations, as determined by neutron activation analysis. Calcium concentrations were 0.90% in the lower-protein diet and 1.00 to 1.15% in the higher-protein diet, as fed. Heaney (1998) argued that if Ca intake is sufficiently high, excessive dietary protein will not result in bone loss; he contended that the ratio of dietary Ca to protein is more important than the absolute dietary concentration of Ca. A ratio that was proposed as adequate to prevent bone loss was about 20 mg of dietary Ca per gram of dietary protein, although the suitability of that ratio has not been experimentally confirmed in nonhuman primates. In any case, it is likely that Ca requirements of nonhuman primates will vary to some extent with dietary habits and composition of the diet, as they do in humans (Nordin, 2000).
A diagnostic distinction between protein-calorie malnutrition and Ca deficiency was noted when cadmium was administered to rhesus macaques. Metallothionein (MT) production was induced, but the major liver isoform was MTc in protein-calorie malnourished monkeys and MTb in Ca-deficient monkeys (Nath et al., 1987).
As early as 1957, a relationship of bone loss, a decrease in effective Ca use, and restricted physical activity in humans was reported (Whedon and Shorr, 1957). Physical restriction of Macaca nemestrina also increased Ca excretion (Pyke et al., 1968). Osteoporosis and osteoarthritis might be more common in chronically physically restricted primates (DeRousseau, 1985a,b; Pritzker et al., 1985; Rothchild and Woods, 1992), although some authors question the occurrence or incidence of osteoarthritis in nonhuman primates (Ford et al., 1986; Jurmain, 1989; Chateauvert et al., 1990; Sokoloff, 1990). When over 1,500 nonhuman-primate skeletons of 29 species were examined, osteoarthritis was more prevalent in captive animals (presumably physically restricted) than in wild animals (Rothschild and Woods, 1992). Eaton and Nelson (1991) have proposed that Ca intakes of humans living at the end of the Stone Age were twice those of contemporary humans, and their physical exertion was greater than at present. Skeletal remains suggest that Stone Age humans developed a greater peak bone mass and experienced less age-related bone loss than 20th Century humans.
Many of the diets fed to captive nonhuman primates comprise mixtures of nutritionally complete biscuits or pellets, fruits, vegetables, browse, and insects. However, given the opportunity for free choice among such an assortment of foods, the likelihood of Ca deficiency is real. With the exception of primate biscuits and some green, leafy vegetables, most of those foods are inadequate sources of Ca. In spinach, much of the Ca is bound to oxalate and unavailable. Sprinkling on Ca supplements does not necessarily prevent Ca deficiencies that might appear when mixed diets are fed. That practice was attempted with two species of lemurs (Lemur catta and L. variegatus) at the Cincinnati Zoo, but much of the supplement did not adhere to the foods; signs of nutritional secondary hyperparathyroidism were seen, including hyperphosphatemia, hypocalcemia, increased alkaline phosphatase activity, impaired mobility, bowing of the long bones, poorly mineralized skeleton, and soft tissue mineralization (Tomson and Lotshaw, 1978).
Nursing neonatal New World and Old World primates, with presumably adequate Ca intakes from milk, presented signs of abnormal Ca status (Ullrey, 1986; Morrisey et al., 1995). Responses to UVB exposure or to intramuscular vitamin D injections made it look as though vitamin D supplies were inadequate to support normal Ca absorption and metabolism. The milk of species that have been examined is low in vitamin D; if solid food containing vitamin D is not consumed in sufficient amounts or if there is no UVB exposure, absorbed Ca might be inadequate to meet tissue needs. Because of solar UVB exposure, that is proba-