Too much vitamin D may be just as bad as too little, a recent study suggests.

Vitamin D supplements reduce blood levels of C-reactive protein, or CRP, an indicator of inflammation that is linked to cardiovascular disease. But supplements help only up to a point.

In a study of more than 15,000 adults ages 18 to 85, researchers at Johns Hopkins University found that after blood levels exceeded 21 nanograms per milliliter — the lower end of what is usually considered normal — any additional vitamin D led to an increase in CRP.

The association held after the researchers accounted for the effects of factors like obesity, smoking, cholesterol and high blood pressure. There was also a dose-response relationship: Above 21 units, each 10-unit increase in vitamin D was accompanied by an increase of 0.06 milligrams per deciliter in CRP.

“Vitamin D is good to a certain level,” said the lead author, Dr. Muhammad Amer, an assistant professor of medicine at Johns Hopkins. “But don’t just keep on taking it. Have your blood drawn and your levels checked.”