Summary
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What does vitamin D do?
There are many reasons to make sure you're getting sufficient, but not excessive, vitamin D: These include improved bone health, reduced risk of heart attack and stroke, reduced risk of asthma and allergy, reduced inflammation, possibly, a reduced risk of prostate cancer, and perhaps others. Not surprisingly, over given periods of time there are fewer deaths among people who have the right amount of vitamin D compared to those who have too little or too much. For details, see What It Does. -
How much vitamin D do I need?
You may already get enough vitamin D from the sun (about 15 minutes to the face, arms, and hands at least twice a week without sunscreen) and the foods you normally eat. The recommended daily allowance is 15 mcg (600 IU) for teens and adults, going to 20 mcg (800 IU) for those over age 70. If you're not sure, get your blood level checked by your doctor. A total serum 25-hydroxyvitamin D level of at least 20 ng/mL (equivalent to 50 nmol/L) is considered "sufficient," although there may be additional benefit to being in the 25 to 35 ng/mL range. Don't exceed 39 ng/mL. Be aware that people who are Black generally have lower total vitamin D levels than whites, but research suggests these lower levels may be sufficient for Blacks. For details see How Much Do You Need and How Much is Too Much? -
What form of vitamin D is best?
Vitamin D2 or D3 will raise your vitamin D level, but D3 is preferable as it may raise levels more effectively over time and is less likely to cause erroneously low vitamin D blood test results.
Vitamin D supplements are sold as tablets, chewable tablets, capsules, gummies, softgels or liquids. Vitamin D sprays are also sold, and can be as effective as a pill or liquid drops, although they tend to be more expensive. 
Which vitamin D supplement is best?
Among the vitamin D supplements that CL tested and Approved for Quality (see What CL Found), CL selected Top Picks based quality, dosage, price, and convenience of use. These include Top Picks for vitamin D-only supplements, as well as vitamin D in combination with calcium, magnesium, vitamin K, and/or boron.-
When to take vitamin D:
Take vitamin D supplements with your biggest meal of the day (the one that contains most fats and oils) as this can increase absorption by as much as 50%! For details, see Take Vitamin D with Food. -
How much vitamin D should I take?
For every 1 ng/mL increase, you'll need to get an additional 100 IU of vitamin D per day (obese individuals may require double the amount, and if you already have an adequate level, enzymes in your body act to make it harder to raise it). For example, if your blood level is 18 ng/mL, taking 1,000 IU of vitamin D daily (or 1,600 IU if you are obese) should get you to about 28 ng/mL. It can take 6 weeks to reach the peak. Keep taking the vitamin D to stay at that level. The tolerable upper intake level (UL) of vitamin D for teens and adults, above which there is increased risk of toxicity, is 100 mcg (4,000 IU). For details, see What to Consider When Using. -
Don't overdo it! Vitamin D safety and side effects:
Studies show that people with the highest levels of vitamin D actually tend to have more bone fractures, fall more frequently, sleep less well, and die sooner than those with lower, but sufficient, levels. If your level is over 20 ng/mL, you probably don't need a supplement. If your level is above 35 ng/mL, taking a supplement may be doing more harm than good, so consider cutting back. For details see How Much Do You Need and How Much is Too Much?
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