Vitamin D is called the sunlight vitamin because the body produces it when the sun's ultraviolet B (UVB) rays strike the skin. It is the only vitamin the body manufactures naturally and that is technically considered a hormone. Essential for building strong bones and teeth, vitamin D also helps to strengthen the immune system and may prevent some types of cancer.
The trend in the United States in recent years years has been to avoid exposure to sunlight in order to prevent skin cancer. However, this trend is worthy of further scrutiny. While excessive sunlight may be unhealthy for some people, it needs to be remembered that the action of sunlight on the skin is a major source of vitamin D for many people. A lack of sunlight can lead to vitamin D deficiency rickets in children and osteomalacia in adults.
Rickets in children was a wide spread problem in smoggy, industrial urban areas in the early nineteen hundreds, especially in England. It has been suggested that Tiny Tim, the crippled child in Charles Dickens' A Christmas Carol, may have suffered from a case of rickets.
There is the custom of children getting a daily dose of cod liver oil in winter months. The reason for this was to prevent rickets from a deficiency of vitamin D. The health benefits of cod liver oil is that it is one of the few foods with appreciable amounts of this important vitamin.
Beginning in the 1930s, the dairy industry in the United States fortified milk with vitamin D in order to prevent rickets on a nationwide level. However, some physicians are concerned that rickets may be making an unwelcome comeback in recent years due to the trend of avoidance of sun exposure for children combined with the growing popularity of rice and soy based beverages, which may not always be vitamin D fortified. A study conducted in the late 1990s in Georgia found that about one in 200,000 children in that state was hospitalized with rickets.
Signs of vitamin D deficiency rickets include: soft bones, pectus excavatum (sunken chest), pectus carnitum (barrel chest), bowed legs, beaded ribs, ankle and wrist flares, enlarged forehead, stunted growth, fractures, restlessness, irritability, sweaty head, scoliosis, muscle weakness, delayed dentition, infants walk or crawl late.
Besides rickets, other conditions that have been linked to vitamin D deficiency include: some forms of cancer, including breast cancer and colon cancer; osteopenia; osteoporosis; muscular weakness; joint pain; muscle twitching.
Vitamin D deficiency has been associated with insulin deficiency and insulin resistance. In fact, it was shown that vitamin D deficiency is likely to be a major factor for the development of type one diabetes in children. Insulin resistance is also one of the major factors not only leading to the cancers mentioned above, but also to the number one killer in the US, heart disease. Northern countries have higher levels of heart disease and more heart attacks occur in the winter months.
For most people sunlight interacting with oils on the skin is a major source of vitamin D. As to other sources of vitamin D, in general, few foods contain its appreciable amounts. Foods that do contain the vitamin include fortified milk, dark green leafy vegetables, eggs, fish liver oils, butter, tuna and salmon.
As with almost any vitamin or mineral, excessive amounts of this nutrient may have as many negative health consequences as with a deficiency.