Calcium and Vitamin D

Calcium Homeostasis

Calcium is used universally as an adjunct with other treatments and should be included in all interventions to prevent bone loss. Calcium is regulated by three major calcium-regulating hormones: parathyroid hormone, calcitriol, and calcitonin. Parathyroid hormone is the most important regulator of serum calcium concentrations; increasing serum calcium produces a rapid decrease in parathyroid hormone, and vice versa. Parathyroid hormone increases serum calcium concentrations via several mechanisms, including increased resorption from bone. Administration of adequate amounts of calcium offsets the obligatory losses through the urine and feces, thereby preventing synthesis of parathyroid hormone and resultant bone loss of calcium caused by hyperparathyroidism.⁴ A decrease in calcium absorption with aging may partially explain why older patients are prone to developing osteoporosis, by increasing the probability of a negative calcium balance.

National Institutes of Health (NIH) Recommendations for Optimal Calcium Intake

Because of calcium's beneficial effects on achievement of peak bone mass and modifying bone loss, the National Institutes of Health (NIH) convened a consensus conference to formulate recommendations on optimal calcium intake.⁵ The group's recommendations are given in this table.

The body's calcium requirements are mostly determined by skeletal requirements, which contains 99 percent of total body calcium. Higher calcium intake is unlikely to confer any additional benefit, since body retention of calcium increases up to a threshold, after which the additional amounts are excreted.

Available Products/Salts

	Calcium Salt		% Calcium		Tablets for 1000 mg.
	Calcium Carbonate		40		2-3
	Tricalcium phosphate		39		2
	Calcium acetate		25		4-16
	Calcium citrate		21		2-5
	Calcium lactate		13		12-14
	Calcium gluconate		9.3		11-22
	Calcium glubionate		5.5		9mL (available as liquid only)

In general, calcium carbonate is the preferred salt form of calcium, because of its high percentage composition of elemental calcium (meaning fewer tablets need to be taken) and low cost.⁶ The carbonate, and citrate salts are also available in liquid formulations, while the glubionate form is available as a liquid only. Calcium carbonate is also available as a chewable tablet. Individuals in whom diminished gastric acidity is suspected (e.g., the elderly, those with achlorhydria, or those receiving therapy with histamine-2 receptor antagonists or proton pump inhibitors) should probably receive a more soluble calcium salt, such as calcium citrate.

Vitamin D Recommendations

The physiologic effects of vitamin D include an increase in calcium and phosphorus absorption from the small intestine, a reduction in urinary calcium excretion, and maintenance of serum calcium and phosphorus concentrations through mobilization of bone minerals. The latter effect explains why excessive intake of vitamin D may actually cause osteoporosis. Its major action in prevention of bone loss probably results from its improvement in calcium absorption, with a resultant decrease in parathyroid hormone secretion and bone resorption.⁴

Elderly individuals are often vitamin D deficient due to low dietary intake, lack of exposure to sunlight, and/or impaired renal synthesis. Recent studies have indicated that vitamin D deficiency is common among elderly patients admitted to hospitals for hip fracture. ^8,9 Moreover, hypovitaminosis D is common in the general medical inpatients, including those with vitamin D intakes exceeding the recommended daily allowance and those without apparent risk factors for vitamin D deficiency.¹⁰

The NIH recommends that a vitamin D intake of 600 to 800 IU/should be ensured in all individuals (milk contains about 100 IU per cup). The recommended calcitriol dose is 0.25 mcg/day.⁵ Vitamin D does not need to be given simultaneously with calcium in order to be effective. Oversupplementation should be avoided, as it may lead to hypercalcemia, hypercalciuria, polyuria, renal stones, renal failure, and ectopic calcium deposition. Excessive vitamin D intake may also cause osteoporosis because of excessive mobilization of bone minerals.

The NOF¹ and AACE⁷ Guidelines state that adequate intake of calcium and vitamin D is fundamental to all prevention and treatment programs for postmenopausal osteoporosis, and that supplements should be used when necessary to ensure adequate intake. Adequate calcium and vitamin D intake should be maintained for lifetime.

Clinical Trials

Trial in Nursing Home Elderly

CALCIUM AND VITAMIN D: EFFECT ON NONVERTEBRAL FRACTURES IN ELDERLY WOMEN:18 MONTH STUDY

The most convincing evidence to date of the utility of calcium and vitamin D in elderly women comes from a controlled study¹¹ comparing the administration of placebo or 1200 mg of calcium (as tricalcium phosphate) plus 800 IU of vitamin D3 daily in 3270 women aged 69 to 106 years. Active treatment led to a 32 percent reduction in nonvertebral fractures (excluding the hip) and a 43 percent reduction in hip fractures. Femoral bone density increased 2.7 percent in the active treatment group versus decreasing 4.6 percent in the placebo group. The serum parathyroid hormone concentration decreased from baseline in the calcium-vitamin D group, whereas it increased in the placebo group, lending credence to the theory that excessive parathyroid activity plays a role in the pathogenesis of bone loss.

Trial in Community-Dwelling Elderly

A more recent double-blind, placebo-controlled study¹² investigated daily dietary supplementation of 500 mg calcium plus 700 IU of vitamin D3 over a three year period in 389 community-dwelling men and women 65 years of age or older. Active treatment at the end of three years showed a decreased incidence of first nonvertebral fractures in the treatment group (12.9 percent in the placebo group and 5.9 percent in the calcium-vitamin D group). In both men and women calcium-vitamin D supplementation reduced total-body bone loss compared with placebo.

At the present time, there is little evidence to support fracture reduction with vitamin D and calcium supplementation if there is no evidence of a deficiency of these nutrients.¹³

A recently published trial studied the effect of 10,000 IU of vitamin D given every four months for a period of five years (15 total treatments) in community-dwelling people over 65 years old. The authors concluded that the treatment resulted in 22% lower rate for first fracture at any site and a 33% lower rate for a fracture occurring in the hip, wrist or forearm, or vertebrae. So in conclusion, four monthly supplementation with 100 000 IU oral vitamin D may prevent fractures without adverse effects in men and women living in the general community.^13a

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