Can Summer Sun Give Enough Vitamin D? Probably not. Even if you live in a warm climate, you may need to supplement it with vitamin D. A reputable doctor explains why.

"Most people don't get enough sun exposure without protection to make enough vitamin D," says Ken Redcross, MD, a holistic physician and author of Bond: The 4 Cornerstones of a Lasting and Caring Relationship with Your Doctor.

Can Summer Sun Give Enough Vitamin D?

Based on his years of research and experience in testing patients' vitamin D levels regularly, Redcross estimates that 80-90 percent of Americans are deficient in sunlight vitamins, even in warm Southern states. Fatigue, anxiety, recurrent infections, and feelings of "not oneself" are common signs.

Science says that vitamin D is a "prohormone," which means a hormone precursor. Redcross explained it this way: "Think of it as the key to unlocking the gene that has healing power."

Most immune cells need vitamin D to do their job, and that's important for heart, muscle, bone, and mood health, and to ward off diabetes as well as autoimmune conditions.

When people take enough vitamin D for 4-6 weeks, they usually have more energy and feel better overall. "They're experiencing a new sense of well-being," Redcross said.

Then, how many doses are enough? Everyone has a different dosage, but Redcross recommends taking 5,000 IU (125 mcg) daily.

Vitamin D Testing and Dosage

Ask your doctor for a vitamin D test—a simple blood draw—that insurance may be dependent on. The at-home test, using a nearly painless finger prick test kit, is available for about $65 from nutrientpower.org.

Once you've got the test results, use the calculator on the site to identify the dose of vitamin D needed to reach optimal levels of 40–60 ng/mL (nanograms per milliliter)