There is much controversy over the role of vitamin D in many diseases and conditions besides its effect on calcium intake and bone metabolism. This is a brief introduction to vitamin D. You can find much more concerning all aspects of vitamin D in my book Vitamin D for Dummies.
First of all, vitamin D is not actually a vitamin, but rather a hormone. A vitamin is, by definition, a food substance that cannot be made in the body and must be taken in from an external source. In fact, the human body exposed to sunlight can make all the vitamin D it needs. Unfortunately, the fear of skin cancer has resulted in avoidance of sun exposure, so that many people must take a supplement to achieve the necessary vitamin D level. In the winter and above certain latitudes you get very little ultraviolet B light, the kind that makes vitamin D, so you have to take a supplement then as well. It is difficult to get enough vitamin D from food.
Secondly, many conditions have been shown to be reduced in people who have adequate lifelong blood levels of vitamin D. They include the following:
- Cancers: Colorectal, prostate and breast
- Infectious diseases: Tuberculosis, influenza, upper respiratory viruses
- Autoimmune diseases: Multiple sclerosis, rheumatoid arthritis, systemic lupus erythematosis
- Heart disease: Coronary artery disease, high blood pressure, heart failure
- Metabolic disease: Types1 and 2 diabetes, metabolic syndrome, polycystic ovary syndrome
- Other possible diseases prevented by adequate vitamin D: Asthma, psoriasis, autism, Alzheimer’s’ disease, Parkinson’s disease, depression, seasonal affective disorder
While the evidence for the role of vitamin D is stronger for some of these diseases than others, all of them are currently being studied to see if vitamin D can prevent their onset.
Thirdly, while the blood level of vitamin D necessary to prevent these diseases is not known, many experts feel that current government recommendations are woefully inadequate. Levels above 20 nanograms/milliliter (ng/ml) are considered sufficient because this is the level that prevents bone disease, but levels above 30 ng/ml or greater may be necessary for the prevention of the conditions listed above. Vitamin D is very inexpensive and daily intake of 2000 international units (IU) is not excessive.
Fourthly, it is very difficult to take an overdose of vitamin D, except in babies and small children. Adults who are deficient are often given 50,000 international units a week to make up for the deficiency without a problem.
While it is true that a major study is looking at the role of vitamin D and prevention of disease, I am not waiting around for the results of that study. As a physician in practice, I have always used the least amount of medication for my patients that is necessary, but I take my 2000 international units of vitamin D daily.