Vitamin D and Bone Health
Vitamin D (calciferol) is important for bone health. It's major function is to aid in the absorption of calcium and phosphorous, which are two important bone minerals. Vitamin D is synthesized by the skin in response to exposure to the UVB rays of sunlight. In addition, milk and breakfast cereals are often fortified with vitamin D. It also occurs in some foods such as fatty fish and fish oils and from the eggs of hens that are fed vitamin D.
Vitamin D Deficiency
Because Vitamin D is synthesized in the skin, young persons living in sunny areas will rarely be deficient. However, using sunscreen will prevent or lessen vitamin D synthesis, as will the skin pigment melanin. This means that in general, fairer skinned people will synthesize more vitamin D in response to sunlight than darker skinned people. That is, if they aren't wearing sunscreen.
Persons who may be at risk of a deficiency are those that live in a location during the winter months where the sun rarely shines or in certain latitudes where the sun is weak during the winter months, such as places like Boston, Massachusetts, for example. It has been found that sun exposure during the winter months in Boston isn't sufficient to promote vitamin D synthesis in the skin (Webb et al., 1988).
The elderly is particularly at risk for vitamin D deficiency. People 65 years of age and over produce four times less Vitamin D in their skin than younger persons (Van Staveren et al., 2002). This means that elderly persons, especially those than don't get outdoors much, have an increased risk of deficiency.
In addition, because human breast milk doesn't contain vitamin D, breast fed infants may be at risk. Be sure to check with your pediatrician before supplementing an infant with any kind of vitamins or supplements.
Problems associated with vitamin D deficiency are:
- decreased calcium and phosphorous absorption
Can You Take Too Much?
Because Vitamin D is a fat soluble vitamin and can accumulate in the body you can take too much. You don't have to worry about making too much vitamin D in your skin because your body has feedback mechanisms that will shut down vitamin D production once you have reached a certain level. Ingesting too much through foods is also unlikely. However, it is possible to get too much through the use of supplements.
Getting too much vitamin D can lead to health problems such as the following:
- Reduced Renal Function
- Blood calcium levels that are too high
- Nausea and vomiting
- Hardening of soft tissues, such as the heart, blood vessels, and lungs
Should You Take a D Supplement?
Adequate intake for vitamin D is 200 IU for children and adults up to 50 years of age, 400 IU for those aged 51-70, and 600 IU for persons age 71 and older(NIH, 2007). The upper tolerable limit for Vitamin D is 2000 IU for persons aged 1 year and older (NIH, 2007). The upper tolerable limit is only 1000 IU for infants 1 year and younger.
Keep in mind that if you take a daily multivitamin, such as Centrum, that it contains 400 IUs of vitamin D. Then, if you drink fortified milk, juice, or eat fortified cereal and then take a vitamin D supplement then you may get close to or exceed the upper tolerable limit and begin to have health problems. In addition, if you go outside you may also produce some vitamin D on your own. Don't forget that a lot of calcium supplements also contain vitamin D.
However, despite all of the sources of vitamin D mentioned above and the risk of toxicity with supplement use, there are still a lot of people that are deficient in vitamin D that will benefit from supplementation. It is estimated that 47 percent of elderly women and 36 percent of elderly men are deficient in vitamin D (Van der Wielen et al., 1995). This can translate into an increased risk of bone fractures among the elderly. This deficiency could be prevented by supplementation, especially during the winter months. This deficiency probably stems from them not taking a multivitamin, which I would recommend for everyone. By taking a daily multivitamin you get a wide range of all of the vitamins and some minerals, but not so much of any one kind that you have to worry exceeding the upper tolerable limit. In this way, you will be deficient in nothing, but you will still be well within the safety limits for any particular vitamin. However, if you are above the age of 71 make sure that you get the extra 200 IUs needed for your age group (providing that your multivitamin contains 400 IU of vitamin D. If you choose not to take a daily mulivitamin for some reason just be sure that you are getting at least your minimum daily requirement of D, but not exceeding the upper limit of safety.
In recent years, more benefits of Vitamin D have really become known. Vitamin D helps to prevent a variety of diseases, such as multiple sclerosis and also enhances immune function, thereby helping to prevent cancer. The best Vitamin D is that you make yourself when your skin is exposed to sunlight. So put on your shorts and flip flops and expose yourself to a little sunshine each day to make some Vitamin D.
National Institutes of Health (NIH) (2007). Office of Dietary Supplements.
van der Wielen, R.P.J., Lowik, M.R.H., van den Berg., de Groot, L.C.P.G.M., Haller, J., Moreiras, O., and van Staveren, W.A.(2002). Serum vitamin D concentrations among elderly people in Europe. Lancet 346: 207-210.
van Staveren, W.A., and de Groot, L.C.P.G.M. (2002). Vitamin D: Nutritional significance. In Encyclopedia of Dairy Sciences, H. Roginski, J.W. Fuquay, P.F. Fox (Eds.), London: Academic Press.
Webb, A.R., Kline, L., and Hollick, M.F. (1988). Influence of season and latitude on the cutaneous synthesis of vitamin D3: Exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. The Journal of Clinical Endocrinology and Metabolism 67: 373-378.