Three-quarters of adults have a vitamin D shortfall, and with sunshine in short supply, you may be looking for a supplement. Here's help!

By Mirel Ketchiff
December 22, 2014

At least 77 percent of American adults have low levels of vitamin D, according to research in JAMA Internal Medicine -and many experts believe deficiencies are even more common in the winter, when our skin is rarely exposed to the sun. That's a problem, since shortfalls in "the sunshine vitamin" have been linked to some pretty scary outcomes, including soft bones, seasonal affective disorder and even an increased risk of death from issues like cancer and heart disease.

The easy fix? Supplements. (Bonus: They can boost athletic performance too.) But not all vitamin D pills are created equal, as a recent review of 23 vitamin D-containing products conducted by independent testing company found. (Shape readers can get 24-hour access to the report, which is usually under a paywall, here.) So we asked president Tod Cooperman, M.D., how to spot the safest, most effective options out there.

Rule #1: Remember, more isn't always better

First things first: Yes, it's hard to get vitamin D in the winter and yes, shortfalls have some scary side effects, while supplementing has pretty great-sounding perks (like warding off weight gain, for one). But getting too much vitamin D can also be harmful, says Cooperman. Your safest bet, he says, is to get your vitamin D levels tested before choosing a dose. Until you can, avoid taking more than 1,000 IU per day and beware of signs of vitamin D toxicity, like nausea and weakness.

Rule #2: Look for third-party certification's report found that some supplements contained more than 180 percent more vitamin D than their labels stated, which-as Cooperman pointed out above-can increase your risk of an overload. Other research published in JAMA Internal Medicine had similar findings, and the study authors offered an easy enough fix: Check vitamin D bottles for a USP verification seal, which indicates the supplement went through voluntary independent quality testing. These pills listed their amounts most accurately.

Rule #3: Opt for liquids or gel caps

There's a small risk that caplets (coated pills-they're general solid colored) won't break apart in your stomach, which inhibits the amount of vitamin D you actually absorb, says Cooperman. "But that's not an issue with capsules, soft gels, liquids, or powders." (What you eat when you take it also affects absorption. Are You Taking Your Vitamin D Supplement Wrong?)

Rule #4: Go for vitamin D3

There are two forms of supplemental vitamin D-D2 and D3. Cooperman recommends going with the latter, since it's the type of D that's produced naturally by our skin and is therefore slightly easier for the body to absorb. If you're vegan, however, you may be better off opting for the D2, since it's produced using yeast or mushrooms; D3 is often made from a derivative sheep's wool.