Nancy's Nutrition Corner

"Let food be thy medicine and medicine be thy food," Hippocrates.

Vitamin D, The Sunshine Vitamin

The other day I was eating some delicious garlic fries at Johnny's--a hip harbor-side cafe here in Santa Cruz. As I was eating them, enjoying their crispy texture and golden flavor, I couldn't help but think about the possibility of greasy free radicals from those French fries wreaking havoc on my coronary arteries. This is the problem when you have too much clinical nutrition information in your head — you can no longer unconsciously enjoy junk food. I imagine we are all faced with such dilemmas as we make our food choices. There is often a struggle between what we desire and what we know would be a better choice. Sometimes we just have to default to the fries. Even so, I would like to play a role in promoting conscious eating in the hopes of encouraging good food choices. For this reason, I'd like to shift the focus of this year's articles to the individual nutrients: what they do for us, and where to find them.

Let's start with Vitamin D...

Role in the body
There are receptors for vitamin D in a wide variety of tissues and organs including the intestines, bone, kidney, heart, muscle, brain, and immune system. Vitamin D stimulates the production and differentiation of many types of cells in the body, especially those involved in the production of bone and those of the immune system.

Vitamin D has a well known role in mineral metabolism and bone growth. In the small intestine, vitamin D increases intestinal absorption of calcium and phosphorous. When vitamin D levels are low, the absorption of calcium and phosphorus drops dramatically. In the absence of sufficient vitamin D, only about 10% of calcium and 60% of the phosphorus consumed are absorbed! Diminished absorption of these minerals is reflected in low bone mineral density--which is associated with osteopenia, osteoporosis, and decreased muscle strength.

Vitamin D receptors have been identified in cells critical to the immune system. Vitamin D inhibits the growth of some cancers, plays a role in the body's response to infectious diseases, and modulates autoimmune diseases. It does this by its involvement in the function and development of T-cells. T-cells are responsible for identifying pathogens and coordinating immune responses. Vitamin D deficiency leads to a decreased production of these white blood cells.

A recent review article in the New England Journal of Medicine concluded that vitamin D deficiency is widespread. An estimated one billion people have insufficient levels of the vitamin.

This widespread deficiency is due to several factors. First, most people's diets do not include the RDA (required daily allowance) of vitamin D. Second, many common medications can deplete stores of vitamin D; these include some ulcer medications, cholesterol lowering drugs, corticosteroids, and several anticonvulsants. Finally, since the body can create vitamin D if given sufficient exposure to sunlight, the increased use of sunscreen has lessened many people's vitamin D levels.

Deprivation of vitamin D leads to impaired absorption of calcium and phosphorus. Without sufficient calcium and phosphorus the mineralization of bones cannot occur and the bone matrix becomes progressively de-mineralized, resulting in "soft bones", i.e.; osteopenia and osteoporosis.

It is also important to note that individuals living at higher latitudes are unable to produce adequate amounts of vitamin D. People living in these regions have been found to be at greater risk of certain cancers including colon, pancreatic, prostate, ovarian, breast, and Hodgkin's lymphoma.

Include it in Your Diet
Excellent sources for vitamin D are oily fish such as salmon, herring, sardines and cod liver oil. Good sources include fortified milk, bread and cereal products. Other sources include mushrooms, shrimp and eggs (sounds like a yummy omelet to me!). Another excellent source is exposure to sunlight. Vitamin D is formed in the skin by the action of shortwave UV light. About 15 minutes of exposure on the face, hands and arms at least three times a week in the spring, summer and fall will provide adequate vitamin D and allow for storage in the body's fatty tissue for the winter months. One important note: sunscreen of SPF8 reduces production of vitamin D by 95%! It is estimated that moderate sun exposure without sunscreen could prevent 30,000 cancer deaths in the United States each year.

Nancy Silva, ND is a licensed naturopath with a penchant for good food. Her monthly column discusses the nutritional aspects of some of the foods available through LocalHarvest. You can contact Nancy from her listing on our website.

Back to the January 2009 Newsletter