Vitamin D, (which is actually a hormone, not a vitamin), is critical for our musculoskeletal health. It helps the body absorb calcium from the small intestine, and therefore is essential for bone formation. However, since 2000, there has been an increase in research into the possible non-skeletal benefits of vitamin D (1), and along with that, we’ve seen a significant increase in sales and (sometimes) hype about these supplements.
What it does and doesn’t do, and the controversy over how much we need, is the subject of this month’s blog. I have outlined the facts as we know them today.
The Sunshine Vitamin
Of all the many vitamins we need, Vitamin D is the only one we can make ourselves. This occurs when the skin is exposed to sunlight. We know that about 15 to 20 minutes of midday sunlight to the face, neck and arms 3 – 4x/week will generally produce sufficient amounts of vitamin D. But this “rule of thumb” changes if:
- you live in northern regions and/or its winter. In the US, the line of demarcation is the 37th. Picture a horizontal line drawn from Philadelphia → Columbus, Ohio → Denver → Sacramento. One study reported a 4% increment in hip fracture incidence for each 1˚ latitude difference from the equator (2). Also, not only are we bundled up in colder months with little skin exposure, but between November to March, and in northern regions, the sun is lower in the sky.
- you live in a smoggy city. Atmospheric pollution blocks the ultraviolet rays.
- you have darker skin. The pigment (melanin) in dark skin doesn’t allow the skin to absorb as much UV radiation.
- you are over 60. After age 50, the body’s ability to make vitamin D declines. Once over age 65, you generate only one-fourth as much vitamin D as you did in your 20s.
- you have certain health conditions. Inflammatory bowel disease, celiac disease, and liver disease, for example, may interfere with the absorption of vitamin D.
- you take certain medications. Vitamin D levels can be lowered by certain medications. Examples include laxatives, steroids (such as prednisone), cholesterol-lowering drugs(such as cholestyramine and colestipol), seizure-control drugs (such as phenobarbital and phenytoin), a tuberculosis drug (rifampin), a weight-loss drug (orlistat).
- you are overweight. If your body mass index is above 30, you may have low blood levels of vitamin D. Vitamin D is stored in fat, so in people with obesity, less of the vitamin circulates in the blood, where it’s available for use by the body.
In the above circumstances, much more sun exposure is required to synthesize vitamin D. These factors, in addition to valid concerns about skin cancer, as well as the difficulty of getting adequate amounts from our food, lead many people to require supplementation.
Should You Take a Supplement?
A simple blood test can help you and your healthcare provider decide if supplementation is necessary. The two types of vitamin D (D2 and D3), are changed into a form of vitamin D called 25 hydroxyvitamin D, also known as 25(OH)D. The levels of vitamin D are measured by the 25-hydroxy level in nanomoles/liter (nmol/L), or nanograms/milliliter (ng/mL). This where things get tricky, because you have to pay attention to how the numbers are recorded, (nmol or ng/ml), as you try to interpret your results. Also, keep in mind that not all researchers and healthcare professionals agree with these values.
Current guidelines from the National Institutes of Health (NIH) Office of Dietary Supplements (3), state that the results can indicate the following:
- Levels of 50 nmol/L (20 ng/mL) or above are adequate for most people for bone and overall health.
- Levels below 30 nmol/L (12 ng/mL) are too low and might weaken your bones and affect your health.
- Levels above 125 nmol/L (50 ng/mL) are too high and might cause health problems.
According to the NIH, the National Academy of Medicine (formerly the Institute of Medicine), Harvard Health, the Mayo Clinic, and several other reputable sources, the current Recommended Daily Allowance (RDA) for vitamin D is 600 international units (IU), or 15 micrograms (mcg), per day for adults under age 70, and 800 IU, or 20 mcg, for those over age 70.
Signs and Symptoms of Deficiency
These might include:
- fatigue
- bone pain
- muscle weakness, muscle aches, or muscle cramps
- mood changes, like depression
Is There A Sweet Spot?
There is considerable controversy in the literature about exactly what adequate vitamin D levels should be. An opinion piece in the Journal of Bone and Mineral Research states, “… the evidence pointing to a skeletal need for higher levels….in our collective judgment, indicate that instead of 20 ng/mL, a serum level of 30 ng/mL is closer to the bottom end of the acceptable range for skeletal health” (4).
With all this in mind, my view is to aim for between 30 – 50 ng/mL, with the higher end of this range being preferable.
If You Supplement, Be Careful of Excess
Remember the Goldilocks Principle. As with so many things, more of this essential nutrient is not necessarily better, and can potentially cause harm. Excess amounts have been associated with kidney stone formation, especially when taken with calcium (5), increased risk of falls and fracture (6), and hypercalcemia – a condition where too much calcium builds up in your blood, possibly forming calcium deposits in the arteries and soft tissues.
While rare, toxicity is possible, and some signs of this include confusion, constipation, nausea, poor appetite, vomiting, weakness, weight loss, increased thirst and urination, and ataxia (a neurological condition that may cause slurring of words and stumbling).
Interestingly, you cannot get too much vitamin D from the sun, but overdoing that also has its own serious risks.
Vitamin D Is Not, After All, the Panacea We Hoped For
The bottom line is that we must have enough vitamin D for our bodies to function properly, but taking too much is not helpful. And our hopes that vitamin D would solve many of our health problems have largely been dashed.
A very large, 5-year randomized clinical study of nearly 26,000 healthy women and men called the VITAL trial (VITamin D and OmegA-3 TriAL), investigated whether taking daily dietary supplements of vitamin D3 (2000 IU) or omega-3 fatty acids (1000 mg fish oil) reduced the risk of developing cancer, heart disease, and/or stroke in people who did not have a prior history of these illnesses. A subgroup of 770 subjects were randomly assigned to take vitamin D or a placebo to track the incidence of falls, fractures, and bone health (7).
The key findings were that vitamin D did not reduce risk of cancer, major cardiovascular events (heart attack, stroke), improve bone density, or prevent fractures or falls. (The fish oil supplementation also did not reduce risk of cancer or major cardiovascular events, but did reduce the risk of heart attack by 28%, “when heart attack was considered separately from other cardiovascular events”; the benefit appeared strongest in African Americans.)
Other very large studies have reported similar findings with regard to no benefit in taking extra vitamin D to prevent falls and fractures (8).
But don’t despair! There are countless studies that reveal the proven benefits of EXERCISE when it comes to practically every aspect of our health – from strong bones to a strong heart!
See you in class ?
- Rooney MR, et al. Trends in Use of High-Dose Vitamin D Supplements Exceeding 1000 or 4000 International Units Daily, 1999-2014.Journal of the American Medical Association 2017;317(23):2448–2450.
- Grant WB. Variations in Solar UVB Doses and Serum 25-hydroxyvitamin D Concentrations May Explain the Worldwide Variation in Hip Fracture Incidence. Osteoporosis International 2012 Sep;23(9):2399-400.
- https://ods.od.nih.gov/factsheets/VitaminD-Consumer/
- Heaney RP, et al. Why the IOM Recommendations for Vitamin D Are Deficient. Journal of Bone and Mineral Research 2011 March;26(3):455-457.
- Wallace RB, et al. Urinary Tract Stone Occurrence in the Women’s Health Initiative (WHI) Randomized Clinical Trial of Calcium and Vitamin D Supplements. American Journal of Clinical Nutrition 2011;94(1):270-277.
- Sanders KM, et al. Annual High-Dose Oral Vitamin D and Falls and Fractures in Older Women: A Randomized Controlled Trial. 2010;303(18):1815–1822.
- Manson JE, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. New England Journal of Medicine 2019 Jan; 380:33-44.
- Bolland MJ, et al. Effects of Vitamin D Supplementation on Musculoskeletal Health: A Systematic Review, Meta-analysis, and Trial Sequential Analysis. The Lancet 2018 Nov;6(11): 847-858.