It has long been recognized that vitamin D is not a nutrient in the usual sense, because it is not found naturally in most of the foods that our ancestors consumed. However, people who live in northern latitudes or who do not receive enough sun exposure to synthesize vitamin D naturally in the skin need to supplement their diets with it. Vitamin D became widely known as a nutrient when it was found that fish liver oil supplements, which contain vitamin D, all but eliminated rickets.

The Food and Nutrition Board (FNB) established serum 25-hydroxycholecalciferol (25(OH)D) as the functional indicator for vitamin D in 1997. The RDA of vitamin D is 600 units, an amount that was found to maintain a constant concentration in the body over the winter months. However, this value presumes that the body would have acquired tissue stores of vitamin D during the summer months.

A new study attempted to estimate the amount of vitamin D input required to reach or maintain any given serum 25(OH)D concentration, including that in people without substantial body stores of vitamin D.

It is commonly known by clinicians and investigators that the standard multivitamin dose of vitamin D, which usually contains 400 units/dose, produces little change in measured serum 25(OH)D. Researchers from this study calculated that vitamin D from food and supplement sources should provide less than 15 percent of the total amount required to sustain an ideal serum 25(OH)D.

Therefore, researchers say that the FNB recommendation for vitamin D adds little to the usual daily production in people with a lot of sun exposure and does not provide a sufficient amount to achieve desired 25(OH)D concentrations in those with little sun exposure.

Researchers of this study, some of the top vitamin D researchers in the world, found that a value of 2000 IU vitamin D per day for the tolerable upper input level is still too low. Several other groups have also found that current vitamin D input recommendations are inadequate, leading many to suggest that the currently recommended amounts should be reconsidered.

American Journal Clinical Nutrition January 2003;77:204-210

Dr. Mercola's Comments:

Further confirmation that the recommendation of using cod liver oil, which contains vitamin D, in the winter is wise for most people as the majority of Americans are deficient in vitamin D during the cold weather months. If you haven’t read the first two articles in the links below, please review them for details on vitamin D testing and why vitamin D is important. It is essential to understand that in order to know how much vitamin D you should be taking, you should get your blood level checked. If you use beneficial products like cod liver oil without doing blood tests for vitamin D levels, you should keep the dose at one to two teaspoons per day to prevent overdosing. I have done over 500 vitamin D tests and am now starting to see some patients come back with high vitamin D levels in the middle of winter! I believe this is due to their use of cod liver oil throughout the summer when vitamin D supplementation is usually not needed. This is a major point: excess vitamin D will cause, not prevent, osteoporosis and hardening of your arteries. Please be very careful with cod liver oil. If you are unable to obtain vitamin D testing, then please do not exceed one to two teaspoons of cod liver oil or switch to plain fish oil (no vitamin D) immediately. When choosing a fish or cod liver oil, be sure to choose a brand that has been purified of mercury and other toxins, and has the independent laboratory testing to prove it. I offer Carlson’s brand fish oil and cod liver oil because its high-quality and superior purity and freshness have been proven here in my clinic, whereas I have not been so satisfied with some other brands. You can find the Carlson’s fish oil/cod liver oil in my "Recommended Products" section, or you may be able to find it at your local health food store. Related Articles: Breakthrough Updates You Need to Know on Vitamin D Test Values and Treatment for Vitamin D Deficiency Vitamin D Is Not A Vitamin But A Steroid Hormone Precursor <