Vitamin D, the so-called sunshine vitamin, has generated a lot of attention in recent years. It has been claimed to benefit a wide variety of diseases, everything from cancer to multiple sclerosis. It is widely used along with calcium for bone health. It is added to milk and prenatal vitamins and is prescribed for breastfed babies. Some doctors are recommending everyone take it for prevention. Some CAM advocates are recommending it as a more natural way to prevent the flu than getting a flu shot.
It has been touted as a panacea; Michael Holick even wrote a book titled The Vitamin D Solution: A 3-Step Strategy to Cure Our Most Common Health Problems. Christiane Northrup praised it, saying “This information can save your life. Really.” (Really? I’m skeptical, and her recommendation is not enough to make me want to read the book.) Then there’s Jeff Bowles’ book The Miraculous Results of Extremely High Doses of the Sunshine Hormone Vitamin D3 My Experiment With Huge Doses of D3 From 25,000 To 50,000 Iu A Day Over A 1 Year Period. That one’s not on my reading list either; the tolerable upper intake level is 4,000 IU a day.
It’s hard to avoid the hype and just examine the actual scientific evidence without any bias. The United States Preventive Services Task Force has tried to do just that. It recently evaluated screening for vitamin D deficiency and concluded that the current evidence is insufficient to recommend either for or against screening. Predictably, their announcement has already led to misunderstandings and protests.
What is the USPSTF?
It’s an independent, volunteer panel of national experts in prevention and evidence-based medicine. Its purpose is to improve the health of all Americans by making evidence-based recommendations about clinical preventive services. Its 16 members are appointed by the Director of the Agency for Healthcare Research and Quality (AHRQ) to serve 4-year terms. Candidates are screened to ensure that they have no substantial conflicts of interest, and they come from all areas of primary care, including behavioral health, family medicine, geriatrics, internal medicine, pediatrics, obstetrics and gynecology, and nursing. The biographies of the current members are listed here. In addition to providing recommendations to patients and providers, the Task Force makes an annual report to Congress recommending priority areas for research.
What do their recommendations mean?
Their recommendations are meant as public health measures for the asymptomatic general population; they do not apply to people who have symptoms or are at higher than average risk. They address the evidence-based health benefits and harms of each preventive measure without factoring in costs or economic factors. They are meant as guidelines, not mandates. They are not a one-size-fits all “cookbook.” They are only meant to serve as a starting point for clinicians to use in deciding how to approach prevention for each unique individual patient.
How do they evaluate the evidence?
They have explained their process in detail. They review all available evidence on a subject, try to evaluate all potential benefits and harms, and take into account the quality of the research studies. They then assign a “grade”:
- Grade A: Recommended. High certainty of net benefit.
- Grade B: Recommended. High certainty of moderate net benefit or moderate certainty of moderate to substantial net benefit.
- Grade C: No recommendation. People can opt to use it, but any benefit is likely to be small.
- Grade D: Recommendation not to use. Moderate or high certainty that there is no net benefit or that harms outweigh benefits.
- “I” statement: current evidence insufficient to assess the balance of benefits and harms.
What evidence did they find on vitamin D?
Screening for vitamin D got the “I” statement: the USPSTF felt the evidence was insufficient for a variety of reasons. You can read their detailed reasoning and the research they based it on here, but here are the key points:
- There is no consensus on the definition of vitamin D deficiency.
- There is no consensus on optimal levels.
- Testing methods are not standardized and results vary between laboratories.
- There are no studies evaluating the direct benefit of screening.
- There is adequate evidence that treatment of asymptomatic vitamin D deficiency has no benefit on cancer, diabetes, mortality, or even on fracture risk in persons not at high risk of fracture.
- There is inadequate evidence on the benefit for other outcomes including psychosocial and physical functioning.
- Although the evidence is adequate for a few limited outcomes, the overall evidence on the early treatment of asymptomatic, screen-detected vitamin D deficiency to improve health outcomes is inadequate.
- There are no studies evaluating the direct harms of screening.
- There is adequate evidence that the harms of treatment of vitamin D deficiency are small to none.
The “Discussion” section is illuminating. They cover the effects of vitamin D deficiency, from clear dangers like rickets to less conclusive risks of falls, functional limitations, depression, etc. They cite a study showing that 19% of the US population is at risk for vitamin D inadequacy. They cover risk factors for low vitamin D levels. They point out that dark-skinned people have lower vitamin D levels than whites but that it may be more bioavailable, and they are less likely to have adverse clinical outcomes. Obese people have lower levels, but we don’t know whether they have greater requirements or have greater sequestration into fat tissues. They mention studies showing adverse effects of supplementation, but state that methodological deficiencies in those studies make it difficult to determine actual harms. They plan future updates and may look into risk assessment tools.
Who agrees? Who disagrees?
- No national primary care professional organizations currently recommend routine, population-wide screening for vitamin D deficiency.
- The American Congress of Obstetricians and Gynecologists, the American Geriatric Society, and the National Osteoporosis Foundation recommend testing for vitamin D as part of osteoporosis management or falls prevention.
- The Endocrine Society recommends screening only patients at risk.
- The Institute of Medicine has no guidelines on screening, but recommends an intake of 600 IU a day up to age 70 and 800 IU a day for those over 70.
- The American Academy of Family Physicians agrees with the USPSTF that the evidence is insufficient to assess the balance of benefits and harms of screening the general population, but emphasizes that there are many situations where testing may be indicated, for instance in patients with osteoporosis or malabsorption disorders.
- Several doctors have spoken out against the USPSTF findings.
What’s the harm?
It could be argued that we could just skip the step of testing and have everyone take vitamin D supplements, since they would benefit those who are deficient and would be unlikely to harm those who are not. We add iodine to salt to benefit those who need it, and it doesn’t hurt the rest of us.
That is a reasonable suggestion, but as with everything else in medicine, we shouldn’t jump to conclusions before adequate testing. We might find out that it does more harm than good and/or that it wastes money. Some studies do suggest that there might be adverse consequences of supplementation to high vitamin D levels.
Should you be tested for vitamin D? It would be nice if there were a simple clear-cut answer to that question that would satisfy everyone, but there isn’t. The USPSTF has given us the evidence-based statement that the current evidence is insufficient to recommend either for or against screening. Science can inform us, but it can’t dictate how we should respond to the information. There is room for different responses. Some will choose to screen selected patients with risk factors for low levels of vitamin D. Some will choose to take vitamin D supplements on the precautionary principle, with or without screening tests. Some will decide to spend more time in the sun and risk skin cancer. Some will be content not to screen or supplement until there is better evidence to guide us.
Science-based medicine is complicated. In contrast, CAM frequently appears to be far less complicated. It tends to provide definitive answers that are simple and reassuring. Unfortunately those simple answers all too often turn out to be wrong. Sometimes “I don’t know” is the only reasonable answer.
This article was originally published in the Science-Based Medicine Blog.