From folk remedy of yore to essential nutrient of today - A brief history of vitamin D

Though few people take cod liver oil these days, it was the original source of vitamin D - and the 400 International Units (IUs) contained in a teaspoon of cod liver oil provided some of the basis for today's suggested infant dose (200 IU) of vitamin D. It used to be given to babies to help prevent rickets. Called osteomalacia when it occurs in adults, rickets involves softening of the bones due to calcium loss and, over time, it results in bone deformities, mainly in the knee, wrist and ankle areas.

Although rickets is generally considered a problem of the past, there is growing concern among some North American pediatricians that rickets may be increasing, particularly in people with darker skin and northern Native population. The suspected culprit? Insufficient vitamin D from dietary intake or sun exposure.

Concerns about vitamin D insufficiency extend to adults. Recommended intakes of the 1960s were aimed primarily at preventing rickets in children - adults' vitamin D requirements were not considered. In 1997, these recommendations were revised, thanks to a rapid growth in knowledge about the health benefits of vitamin D and mounting evidence that many Canadians are not getting enough of this nutrient. In fact, the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes tripled the suggested vitamin D intake for people over age 70 (to 600 IU/day), in what is considered the largest ever recommended increase for any nutrient.

How does vitamin D work to promote healthy bones?

Vitamin D works at three sites in the body to regulate calcium levels.

1. In the intestines, it stimulates your body to absorb calcium from the foods you eat (or from supplements).
2. In the bones, it helps incorporate the absorbed calcium into the skeleton for storage and also regulates the cells involved in the process of bone building.
3. It also works in your kidneys to help recycle calcium that would otherwise be excreted in the urine, so your bones can reabsorb it.

So vitamin D's primary effect is to increase the availability of calcium for absorption. Without the help of vitamin D, levels of calcium in the blood, and ultimately in the bone, could be negatively affected.

Vitamin D's direct effect on bone building is demonstrated by the tendency of bone mass to fall faster during the winter and remain fairly stable in the summer, particularly in (but not limited to) northern climates. Research by Dr. Dawson-Hughes and colleagues suggests this seasonal acceleration in bone loss may be offset by supplementation with vitamin D⁽¹⁾ (and other studies^(2,3) suggest that adding calcium may provide additional benefits). Another benefit of vitamin D is that it improves muscle strength and balance so people are less likely to fall. That may be why fracture risk decreases fairly quickly when elderly people start taking calcium and vitamin D, even when bone density has not increased significantly⁽⁴⁾.