And if you need more, many over-the-counter vitamin D supplements range from 25 to 125 mcg (1,000 to 5,000 IU).

Conducted as part of a nationwide four-year trial, the study tracked over 1,000 U.S. adults (men over 50 and women over 55) and found that daily vitamin D3 could reduce biological wear and tear ...

Each was randomly assigned to receive 2,000 IU of vitamin D3 daily, omega-3 fatty acids, a combination of both, or a placebo. Those taking vitamin D saw significantly less telomere shortening.