“Bone health,” says CVS brand vitamin D, which comes in five doses—400 IU, 1,000 IU, 2,000 IU, 5,000 IU, and 10,000 IU. Whoa. The Recommended Dietary Allowance is only 600 IU a day up to age 70 and 800 IU over 70. Do your bones need doses in the thousands? The VITAL trial randomly assigned 25,871 people to take 2,000 IU of vitamin D or a placebo every day for five years. Roughly 770 of the participants had their bone mineral density tested when they entered the study and again after two years.