This large study argues against a lot of extra D, unless moderate doses are not enough to bring your blood levels into the normal range.

Finding the Sunshine Vitamin Sweet Spot

Study after study indicates that coming up short on vitamin D may lead to a range of health woes, from increased risk of heart disease and cancer to osteoporosis, asthma, and allergies. However, as with all nutrients, going overboard with the sunshine vitamin isn’t a good idea either. A comprehensive look at the research on this topic suggests we can best support our well-being by finding the vitamin D sweet spot.

Pooling “D” numbers

To examine the potential connections between vitamin D levels in the blood and mortality—death due to any cause—researchers used meta-analysis to combine and analyze data from 14 previous observational studies on this topic.

The study adds important information to the debate about what blood level of vitamin D promotes optimal health, because the researchers identified a point above which having more vitamin D in the body did not provide any additional benefit.

Normal vitamin D levels range from 75 to 185 nanomoles per liter (nm/L). Using a vitamin D blood level of 27.5 nm/L for comparison, the study authors found that an increase in vitamin D levels:

• from 27.5 to 40 resulted in 14% lower risk of death.
  
  
• from 27.5 to 52.5 resulted in 23% lower risk of death.
  
  
• from 27.5 to 77.5 resulted in 31% lower risk of death.

However, the risk of death did not decrease further if people increased their blood vitamin D levels by more than 87.5 nmol/L above the 27.5 nmol/L reference level (from 27.5 to 115). This suggests that unless a person’s vitamin D level is very low—in the deficient range, or below about 75 nmol/L—there isn’t a benefit to raising vitamin D levels.

Know your numbers

The results from this large study argue against loading up on a lot of extra vitamin D, unless you’ve already determined that moderate vitamin D doses are not enough to bring your blood levels into the normal range. Use our tips to find your vitamin D sweet spot.

• Get tested. Many healthcare providers now test vitamin D as part of routine blood work. If your doctor doesn’t do this, ask if you can get your vitamin D levels tested.
  
  
• Supplement wisely. If your levels are below 75 nmol/L, which is the low end of normal, ask for advice on how much vitamin D you should take. Ask when you should get your blood levels checked again, to make sure the supplements are having the intended effect.
  
  
• Know the conversion. Some labs give vitamin D results in nmol/L, while others give results in nanograms per milliliter (ng/mL). If your results are given to you as ng/mL, multiply this number by 2.496 to get nmol/L. For example, if your vitamin D level is 45 ng/mL, this converts to 112.3 nmol/L, which is in the normal range.
  
  
• Be sun savvy. If you’ve tried vitamin D supplements and your levels are still low, consider getting 10 to 15 minutes of sun exposure per day, which may be a more effective way to increase blood levels of vitamin D for some people. Avoid getting sun between 10 am and 2pm, when the sun is strongest and can cause more skin damage.

(Am J Clin Nutr 2012; 95:91–100)

Suzanne Dixon, MPH, MS, RD, an author, speaker, and internationally recognized expert in chronic disease prevention, epidemiology, and nutrition, has taught medical, nursing, public health, and alternative medicine coursework. She has delivered over 150 invited lectures to health professionals and consumers and is the creator of a nutrition website acclaimed by the New York Times and Time magazine. Suzanne received her training in epidemiology and nutrition at the University of Michigan, School of Public Health at Ann Arbor.

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