Research has told us that Vitamin D deficiency can lead to an increase in inflammation, a leading cause of heart attack and stroke. This is because a "normal" amount of Vitamin D in the blood reduces the amount of CRP, or C-reactive protein, which rises and falls in relation to inflammation.

Supplementation may not be the answer, however, as a recent study at Johns Hopkins University suggested that too much Vitamin D has the same effect as too little.

Researchers examined more than 15,000 adults and found that once blood levels of Vitamin D exceeded 21 ng per mL, what is considered the lower end of "normal", any extra Vitamin D had the opposite effect – it actually increased CRP.

These new findings actually help to make sense of previous research, which showed conflicting results of Vitamin D supplementation. Previous research didn't necessarily take into account the amount of Vitamin D in supplements.

The best course of action is to have your Vitamin D levels checked. If you aren't deficient, then don't take a supplement. If you are deficient, talk to your doctor about how much supplementation you need, and have your levels rechecked regularly. Different people absorb vitamins differently, so the only way to know your levels is to have them checked.

Source: http://www.grannymed.com/news/supplements/vitamin-d-too-much-just-as-bad-as-too-little