Medical Compass: Should you still supplement vitamin D?

By David Dunaief, M.D.

This weekend, we’ll all “Spring forward” to Daylight Saving Time. While we’ll lose an hour of sleep on Sunday, the trade will be more hours of sunshine each day.

If you are like many in the Northeast, this is good news for your vitamin D3 levels. In practice, though, it’s still difficult to get enough sun exposure without putting yourself at higher risk for skin cancer.

There is no question that, if you have low levels of vitamin D, replacing it is important. Previous studies have shown that it may be effective in a wide swath of chronic diseases, both in prevention and as part of a treatment regimen. However, many questions remain.

Many of us receive food-sourced vitamin D from fortified packaged foods, where vitamin D3 has been added. This is because sun exposure does not address all of our vitamin D needs. For example, in a study of Hawaiians, a subset of the study population who had more than 20 hours of sun exposure without sunscreen per week, some participants still had low vitamin D3 values (1).

There is no consensus on the ideal blood level for vitamin D. For adults, the Institute of Medicine recommends between 20 and 50 ng/ml, and The Endocrine Society recommends at least 30 ng/ml.

Does body fat affect Vitamin D absorption?

An analysis of data from the VITAL trial, a large-scale vitamin D and Omega-3 trial, found that those with BMIs of less than 25 kg/m2 had significant health benefits from supplementation versus placebo (2). These included 24 percent lower cancer incidence, 42 percent lower cancer mortality, and 22 percent lower incidence of autoimmune disease. Those with higher BMIs showed none of these benefits.

Does vitamin D increase cardiovascular health?

Several observational studies have shown benefits of vitamin D supplements with cardiovascular disease. The Framingham Offspring Study showed that patients with deficient levels were at increased risk of cardiovascular disease (3).

However, a small randomized controlled trial (RCT) questioned the cardioprotective effects of vitamin D (4). This study of postmenopausal women, using biomarkers such as endothelial function, inflammation or vascular stiffness, showed no difference between vitamin D treatment and placebo. The authors concluded there is no reason to give vitamin D for prevention of cardiovascular disease.

The vitamin D dose given to the treatment group was 2,500 IUs. Some of the weaknesses of the study were a very short duration and small study size, so the results were not conclusive.

How does vitamin D affect mortality risk?

In a meta-analysis of a group of eight studies, vitamin D with calcium reduced the mortality rate in the elderly, whereas vitamin D alone did not (5). The difference between the groups was statistically important, but clinically small: nine percent reduction with vitamin D plus calcium and seven percent with vitamin D alone.

One of the weaknesses of this analysis was that vitamin D in two of the studies was given in large amounts of 300,000 to 500,000 IUs once a year, rather than taken daily. This has different effects.

Does vitamin D help you lose weight?

There is moderately good news on the weight front. the Study of Osteoporotic Fractures found that vitamin D plays a role in reducing the amount of weight gain in women 65 years and older whose blood levels are more than 30 ng/ml (6).

This association held true at baseline and after 4.5 years of observation. If the women dropped below 30 ng/ml in this time period, they were more likely to gain more weight, and they gained less if they kept levels above the target. There were 4,659 participants in the study. Unfortunately, sufficient vitamin D did not result in weight loss.

USPSTF recommendations and fracture risk

The U.S. Preventive Services Task Force recommends against giving “healthy” postmenopausal women vitamin D, calcium or the combination of vitamin D3 400 IUs plus calcium 1,000 mg to prevent fractures, and it found inadequate evidence of fracture prevention at higher levels (7). The supplement combination does not seem to reduce fractures, but it does increase the risk of kidney stones.

When should you supplement your vitamin D3?

It is important to supplement to optimal levels, especially since most of us living in the Northeast have insufficient to deficient levels. While vitamin D may not be a cure-all, it might play a role with many disorders. But it is also important not to raise your blood levels too high (8). The range that I tell my patients to target is between 32 and 50 ng/ml, depending on their health circumstances.

References:

(1) J Endocrinology & Metabolism. 2007 Jun;92(6):2130-2135. (2) JAMA Netw Open. 2023 Published online Jan 2023. (3) Circulation. 2008 Jan 29;117(4):503-511. (4) PLoS One. 2012;7(5):e36617. (5) J Women’s Health (Larchmt). 2012 Jun 25. (6) J Clin Endocrinol Metabol. May 17, 2012 online. (7) JAMA. 2018;319(15):1592-1599. (8) Am J Lifestyle Med. 2021 Jul-Aug; 15(4): 397–401.

Dr. David Dunaief is a speaker, author and local lifestyle medicine physician focusing on the integration of medicine, nutrition, fitness and stress management. For further information, visit www.medicalcompassmd.com or consult your personal physician.