Not only is it important to get enough calcium in the diet, but vitamin D levels in the body are essential to regulate the absorption of that calcium. New research demonstrates that supplements of vitamin D can increase calcium absorption by up to 65%, 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.
The researchers found that calcium absorption was significantly better when there was adequate vitamin D in the blood, compared to when vitamin D levels were in the low end of the “normal” range. Robert Heaney, MD, of Creighton University stated that “the lower end of the normal range of blood vitamin D levels is clearly suboptimal for calcium absorption.”
The researchers say their results 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 much of North America.
Journal of the American College of Nutrition, Vol. 22, No. 2, 142-146 (2003)