What does it do? There are many reasons to make sure you're getting sufficient vitamin D: These include improved bone health, reduced risk of heart attack and stroke, reduced risk of asthma and allergy, reduced inflammation, 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.The right level? 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. 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 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 new 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? 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.How much to 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). For example, if your blood level is 18 ng/mL, taking 400 IU of vitamin D daily (or 800 IU if you are obese) should get you to about 22 ng/mL. It can take 6 weeks to reach the peak. Keep taking the vitamin D to stay at that level. For details, see What to Consider When Using.When to take it? 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.Top Picks: Choose a supplement that has been Approved by ConsumerLab.com in the Results table below because not all supplements live up to their ingredient claims (See What CL Found). Also, see CL's Top Picks for those offering the best value, dose, and convenience.Don't overdo it! 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?You must be a member to get the full test results along with ConsumerLab.com's recommendations and quality ratings. You will get results for 21 vitamin D supplements selected by ConsumerLab.com and 4 others that passed testing in its voluntary Quality Certification Program. In this comprehensive review, you'll discover:Which vitamin D supplements failed our quality ratings and which passed -- including combinations with calcium, magnesium and/or vitamin KCL's Top Picks for vitamin D supplementsWhat vitamin D can and can't do for you, and how too much can actually harm youWhat is vitamin D, and is vitamin D2 or D3 best for you?The best way to take vitamin DWhat is vitamin D deficiency and how to gauge if your vitamin D levels are sufficient, too low, or too high -- and how this may differ if you are blackVitamin D dosage based on your age, gender and needsHow to get vitamin D from the sun and from foods Side effects of vitamin D supplements and potential drug interactions