High intake of vitamin D, is it safe?
Recently I have read a lot about the positive properties of vitamin D. Now I see quantities passing by that are many times higher than what the Nutrition Center recommends. What are the benefits of such a high intake and is it safe?
Vitamin D or calciferol is a group of fat-soluble vitamins, of which vitamin D2 (the vegetable form) and vitamin D3 (the animal form) are the most important. Vitamin D3 is many times stronger than vitamin D2. Vitamin D3 is therefore preferred for humans in the case of supplementation or enrichment.
Your body can form vitamin D under the influence of direct ultraviolet sunlight. In winter you are dependent on the accumulated stock in your fat layer and liver in combination with vitamin D from the diet for vitamin D in the summer. Very few foods are a good source of vitamin D. Actually only fatty fish contain reasonable levels. The dietary requirement for vitamin D depends on the amount of UVB light to which you are exposed. If you don't go outside often or if you wear appropriate clothing, you run a greater risk of shortages. Dark skinned people produce less vitamin D when exposed to sunlight. They are therefore more likely to have a deficiency.
Vitamin D promotes the absorption of the minerals calcium and phosphorus in your body and is important for strong bones and teeth. Vitamin D further helps prevent cardiovascular disease and ensures a strong resistance, proper functioning of the muscles and plays an important role in testosterone production. It is mainly this latter property that makes vitamin D currently of interest to athletes.
In a 2010 Austrian study, 2300 men were examined1. 89% of them were deficient in vitamin D. The results showed that the men with the higher concentrations of vitamin D also had the highest levels of testosterone. Taking a multivitamin preparation had no significant effect on the vitamin D concentration in the body. For that, “multi's” contain too little vitamin D. If you want to achieve an adequate amount of vitamin D in the body, then there are only two options: sunbathe daily or take a strong vitamin D supplement. One should think of a product with a strength of at least 1000 Iu per day
It is virtually impossible to extract toxic amounts of vitamin D from dietary supplements. Vitamin D only has harmful effects with serum values of 250 nmol calcidiol per liter or more. Such values are only achieved with chronic use of more than 10.000 iu (250 mcg) of vitamin D per day. For comparison: People who live in a tropical climate make an estimated 10.000 iu (250 mcg) per day; 100 times more than the recommended daily allowance for adults in the Netherlands!
1 = Wehr E, et al., Association of vitamin D status with serum androgen levels in men. Clin Endocrinol (Oxf). 2010 Aug; 73 (2): 243-8. Epub 2009 Dec 29.