Everyone should consider a daily 1,000- to 2,000 IU supplement as insurance, Manson says. That’s especially key for older adults. “As you age, you make less vitamin D from the sun and absorb less from food,” Pittas says. He recommends a 4,000 IU supplement for those with prediabetes. But taking more could lead to muscle spasms, fatigue, kidney stones, and even coma. So talk with your doctor first.
