Not only is it essential to get enough calcium in the diet, vitamin D levels in the body regulate the absorption of that calcium. New research demonstrates that supplements of vitamin D can increase calcium absorption by up to 65 percent, even when the initial level of blood vitamin D is normal.
Two studies involving 34 healthy, postmenopausal women in Omaha, Nebraska were done one year apart. In one study the women received 500 mg of calcium but no vitamin D supplement. In the other study, the same amount of calcium was given but the women were pretreated for three weeks with vitamin D.
Women were given a calcium supplement and had blood taken at intervals over twelve hours to determine absorption of the calcium with breakfast.
Robert P. Heaney, M.D., of Creighton University, the senior author of the studies stated that "the lower end of the normal range of blood vitamin D levels is clearly suboptimal for calcium absorption. Our evidence points out that low, normal vitamin D status exaggerates the effects of low calcium intake."
These research data are important because they indicate an increased need for vitamin D in the population. Current recommendations for vitamin D intake are 200 International Units (IU) daily for adults up to 50 years of age, 400 IU for those aged 51 to 70, and 600 IU for those over 70 years. The tolerable upper limit in the Dietary Reference Intakes is set at 2,000 IU.
Vitamin D is also made in the skin upon exposure to sunlight. However, concern about skin cancer has caused many people to limit their time in the sun. In addition, during the winter there is an insufficient amount of the sun's rays reaching the skin to stimulate production of vitamin D across the northern half of the United States.
The findings appeared in the April, 2003 issue of the Journal of the American College of Nutrition.