Vitamin D deficiency remains widespread despite the ease of access to modern supplements and fortified foods. According to USA Today, vitamin D3—produced naturally when skin is exposed to sunlight—is the most efficient form for maintaining healthy levels. It helps the body absorb calcium, strengthen bones, and support immune and muscle function.
Experts note that limited sun exposure, higher body weight, age, and certain medical conditions can reduce the body’s ability to produce vitamin D naturally. The National Institutes of Health recommends 600 IU daily for most adults and up to 800 IU for those over 70. Intakes above 4,000 IU from all sources should only be taken under medical supervision.