Two new vitamin D studies offer tantalizing clues about vitamin D and health, though the newly published research challenges long-held assumptions about the sunshine nutrient and bone health. As with most nutrition research, details matter, and considering those details can help you make informed choices about the role of vitamin D in your self-care plan.

Both papers, published in the British Medical Journal, used a technique called meta-analysis, which combines existing studies:

• One paper found people with low vitamin D blood levels were significantly more likely to die from heart disease and cancer compared with people who had higher levels. Supplementing with vitamin D3, though not D2, appeared to reduce risk of death from any cause by 11% in older adults as well.
• The other study supported a connection between higher vitamin D levels and reduced risk of chronic disease. However, the authors concluded that vitamin D supplements alone do not improve bone health and recommended against routine vitamin D supplementation for healthy adults.

Do they stand up to scrutiny?

While meta-analysis may alert researchers to important connections about nutrition and health, the method has downsides. An editorial about the studies noted there is a huge range in type and quality of study included in these meta-analyses, which may lead to erroneous conclusions.

It is possible that low vitamin D levels are caused by disease, rather than disease being caused by low levels, or are an indicator of other factors tied to poor health, such as smoking and obesity.

Considering context

A look at the big picture can help you better understand the connection between vitamin D and optimal health:

• Consider deficiency. Health experts note that as much as two-thirds of the population of the United States and Europe are vitamin D deficient. Considering this and their findings, the study authors reported up to 13% of deaths in the United States and 9% in Europe can be attributed to low vitamin D levels.
• Know your nutrients. Dr. Robert P. Heaney, MD, Professor of Medicine at Creighton University, points out that if a person is low in other critical nutrients, such as magnesium, calcium, vitamin K, or even dietary protein, adding vitamin D is unlikely to improve bone health.
• Supplement wisely. Start with a diet of whole, healthy, unprocessed foods, such as vegetables, fruit, legumes, nuts and seeds, and lean protein. Work with your doctor or dietitian to see where you may be coming up short on critical nutrients, and supplement accordingly.
• Watch the maximums. For most nutrients, health agencies have set safe upper limits of intake. To avoid potential downsides of supplementing, do not exceed these safe upper limits unless directed to do so by your doctor.
• Consider food and supplements. Many people aim to meet all of their nutritional needs with dietary supplements. A smarter strategy? Consider dietary and supplemental sources of key nutrients. Make sure these add up to meet your nutrition goals.

(BMJ 2014;348:g1903; BMJ 2014;348:g2035; BMJ 2014;348:g2280)