Last week I outlined the importance of vitamin D for a healthy body, and how the recommendations for adequate intake published in 2011 were, in retrospect, far too extreme. To understand why vitamin D has played such a major role in the health of the population (vitamin D testing remains the fifth most common laboratory test funded by Medicare), it is worth comparing “observational studies” with “randomized trials.” Observational studies simply point out correlations. Imagine you notice that people who carry lighters in their pockets are more likely to get lung cancer than people who don’t. It doesn’t say that lighters cause lung cancer, it just points out a correlation, and doesn’t mention possible associations such as smoking (this example is from Christopher Lab’s very skeptical book). Does coffee cause cancer? It covers topics such as the Vitamin D controversy.
Nearly a decade ago, numerous observational studies found that low vitamin D levels increased the risk of cancer, cardiovascular disease, diabetes, and falls. But when researchers conducted randomized trials (the gold standard in medicine) with tens of thousands of participants, they found no correlation: People who took a placebo were no different from those who took vitamin D supplements.
This seems like a classic example of “correlation is not causation.” Instead of assuming that low vitamin D levels are the cause of things like cancer and cardiovascular disease, the researchers looked for other factors that could be causing both these diseases and low vitamin D levels. What about something as simple as people who take vitamin D supplements are especially health conscious and motivated to take care of their bodies through exercise, eating right, and getting enough sleep? Or maybe, “if you’re sick, you’re not going outside as much, so you’re not getting your vitamin D from sunlight.”
Dr. Joel Finkelstein, associate director of the Bone Density Center at Massachusetts General Hospital, and his colleagues published a study of more than 2,000 perimenopausal women over a 10-year period. They found that for these women, who are at higher risk of fracture than most because menopause reduces the amount of vitamin D available in the body to strengthen bones, blood vitamin D levels below 20 nanograms per milliliter do indeed increase fracture risk slightly and warrant supplementation. But in contrast to the Endocrine Society’s 2011 recommendations, they say, “For the vast majority of healthy people, levels as low as 15 or even 10 are probably perfectly fine.”
And now, according to a June 3, 2024 press release, the Endocrine Society has (finally) adopted new guidelines: “Healthy adults under 75 years of age are unlikely to benefit from consuming more than the Institute of Medicine (IOM) recommended daily vitamin D intake and do not require testing of vitamin D levels. … For children, pregnant women, adults 75 years of age and older, and adults with high-risk prediabetes, the guidelines recommend a higher daily vitamin D intake than the IOM recommended.” (That equates to 400 IU of vitamin D per day, assuming minimal exposure to sunlight, and “individuals 71 years of age and older may need up to 800 IU per day.”)
In addition to menopausal women, other groups at risk for true deficiency should have their vitamin D levels tested and possibly take supplements, according to Finkelstein’s research. These groups include dark-skinned people who don’t spend much time outdoors, people with anorexia nervosa, people who have had gastric bypass surgery, people with malabsorption syndromes, people diagnosed with osteopenia or osteoporosis, and pregnant and breastfeeding women.
Most of us are healthy and don’t need to take Vitamin D supplements. All of this information is readily available online, in magazines and books, so don’t just take my word for it – your doctor knows best.
Barry Evans (male, [email protected]) is not a medical doctor. Although he is EMT certified, he is not a medical doctor.
