Calcium intake

Magnesium ion is essential for normal Ca " and K" metaboHsm. In acute experimental magnesium deficiency in humans, hypocalcemia occurs despite adequate calcium intake and absorption and despite normal renal and parathyroid functions. Negative K" balance is also observed. AH biochemical and clinical abnormaHties disappear upon restoration of adequate amounts of magnesium to the diet (64). 

Oral calcium has long been used for the treatment of osteoporosis, both in the form of dietary and pharmacological supplements. In patients with calcium deficiency, oral calcium at doses of 1000-1500 mg/day corrects a negative calcium balance and suppresses PTH secretion. Sufficient calcium intake is most important for the acciual of peak bone mass in the young, but is also considered the basis of most anti-osteoporotic regimens. In the elderly, supplementation with oral calcium and vitamin D reduces the risk of hip fracture by about 30 4-0%. 

Some osteoporosis risk factors (see Table 53-1) are non-modifiable, including family history, age, ethnicity, sex, and concomitant disease states. However, certain risk factors for bone loss may be minimized or prevented by early intervention, including smoking, low calcium intake, poor nutrition, inactivity, heavy alcohol use, and vitamin D deficiency. 

A number of factors can limit calcium absorption, and special consideration must be given to calcium dosing to maximize absorption. Large amounts of calcium taken at once cannot be absorbed. Supplement doses should be limited to 500 to 600 mg of elemental calcium per dose. Calcium intake greater than 2500 mg/day should be avoided due to increased risk of toxicity, including hypercalciuria and hypercalcemia. 

Determine average calcium intake from diet (see Table 53-5) and supplements (see Table 53-6). Compare with age-adjusted recommendations (see Table 53—4). Evaluate the patient s sources of vitamin D. 

Counsel the patient to avoid excessive oral calcium intake in vitamin D-mediated hypercalcemia. 

Premenopausal women (mean 40 y) N=170 Observational Urinary mineral excretion Duplicate analyzed samples of coffee, tea, cola Caffeine inversely related to calcium intake and balance, but did not hold up after stratification for calcium intake. 

Fasting ultrafilterable calcium increased and serum bone alkaline phosphatase isoenzyme levels decreased, but only in those with calcium intakes < 600mg/d. 

Caffeine did not have adverse effect in subjects with adequate calcium intakes near or above 800 mg/d, although daily caffeine intake a2-3 servings of brewed coffee may accelerate bone loss from the spine and total body in women with a low calcium intake. 

Picard, D., Ste-Marie, L. G., Coutu, D., Carrier, L., Chartrand, R., Lepage, R., Fugere, P., Damour, P., Premenopausal bone mineral content relates to height, weight, and calcium intake during early adulthood, Bone and Mineral Research, 4, 299, 1988. 

Dietary calcium intake appears to affect lead absorption. An inverse relationship has been observed between dietary calcium intake and blood lead concentration in children, suggesting that children who are calcium deficient may absorb more lead than calcium replete children (Mahaffey et al. 1986 Ziegler et al. 1978). An effect of calcium on lead absorption is also evident in adults. In experimental studies of adults, absorption of a single dose of lead (100-300 ig lead chloride) was lower when the lead was... 

Mahaffey KR, Gartside PS, Glueck CJ. 1986. Blood lead levels and dietary calcium intake in 1- to 11-year old children The Second National Health and Nutrition Examination Survey, 1976 to 1980. Pediatrics 78 257-262. 

Animal studies indicate that nutritional deficiencies in a number of essential elements (e.g., calcium, iron, zinc, copper, phosphorus) may impact the toxicokinetic and toxicological behavior of lead (ATSDR 1993 Chaney et al. 1989). In infants and children, lead retention has been shown to be inversely correlated with calcium intake (Johnson and Tenuta 1979 Sorrell et al. 1977 Ziegler et al. 1978). Zinc has been shown to have a protective effect against lead toxicity in a number of animal species (Goyer 1986 Haeger-Aronsen et al. 1976 Brewer et al. 1985 Cerklewski and Forbes 1976). 

Vatanparast H, Baxter-Jones A, Faulkner R, Baile D and Whiting S. 2005. Positive effects of vegetable and fruits consumption and calcium intake on bone mineral accrual in boys during growth from childhood to adolescence the University of Saskatchewan Pediatric Bone Mineral Accrual Study. Am J Clin Nutr 82 700-706. 

Because excessive caffeine consumption increases calcium excretion, caffeine intake should ideally be limited to two servings per day. Moderate caffeine intake (2 to 4 servings per day) should not be a concern if adequate calcium intake is achieved. 

Calcium Intake Phosphorus Intake Fecal Calcium Apparent Absorption Of Calcium... 

In attempting to reconcile these findings, it should be pointed out that rats may not be appropriate models for the study of calcium metabolism in humans. Unlike humans, the rat does not undergo epiphyseal plate closure and does not have a significant haversian remodeling sequence (21) Furthermore, rats excrete only l-270 of their calcium intake in their urine whereas humans excrete approximately 20-30% or more. This fact is especially significant, since most of the known effects of phosphates on calcium retention in humans are effected by alterations in urinary calcium. 

We have conducted two human metabolic studies (5,6) to compare the effects of increasing phosphorus intake on calcium utilization in healthy young adults maintained at low (ca. 400 mg/day) and high (ca. 1200 mg/day) levels of calcium intake. Increasing dietary phosphorus, as orthophosphate, caused a slight reduction in fecal calcium and a substantial reduction in urinary calcium losses (Table III). 

Condensed (poly) phosphates may exert different effects on calcium utilization than the aforementioned effects of simple (ortho-) phosphates. Polyphosphates have a much greater affinity for calcium than do orthophosphates, and soluble calcium-polyphosphate complexes are readily formed in the gastric and intestinal environments. In addition, polyphosphates must be hydrolyzed by an intestinal alkaline phosphatase (27) prior to absorption. We have found polyphosphates to be incompletely (80.5%) hydrolyzed to orthophosphate during the digestive process in young adult males when calcium intake was low only 56% of a 1 g phosphorus supplement was absorbed from a polyphosphate sources as compared to 71% from an orthophosphate source (5). 

Diet Calcium Intake Fecal Excretion Urinary Excretion Balance... 

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