Participants were randomized into one of four groups, receiving either 200, 1000, 2,000, or 4,000 international units (IU) per day of vitamin D3 supplementation. Blood levels of the markers of ...
Around 600 to 800 IU a day should be plenty, unless your doctor instructs you otherwise. Extremely high levels of vitamin D can lead to irregular heartbeat, kidney failure and death. This is typically ...