The US Institute of Medicine has published new data advising that almost all people take sufficient vitamin D when their blood levels are at or above 20 nanograms per milliliter. Other scientists continue to endorse the older guidelines recommending vitamin D levels above 30 nanograms per milliliter.
To investigate the association between blood vitamin D concentrations and mortality in adults with and with-out chronic kidney disease, (CKD), 25[OH]D levels and all-cause mortality rates were examined in 1,097 adults with, and 14,002 adults without CKD, who participated in the Third National Health and Nutrition Examination Study (1). The study results showed that among the participants with CKD, 76.5 percent had vitamin D blood levels below 30 ng/ml and 35.4 percent had levels below 20 ng/ml. Among adults with healthy kidneys, 70.5 percent had 25[OH]D levels below 30 ng/ml while 30.3 percent had 25[OH]D levels below 20 ng/ml. After adjustment for age, sex, race, health status and season, significantly higher mortality rates were noted among individuals with 25[OH]D levels below 12 ng/ml – among participants with and without CKD – compared to a referent group with 24 to 29.9 ng/ml. Mortality rates were fairly similar across all participants with 25[OH]D levels above 20 ng/ml.
The researchers concluded that since differences in mortality rates across the range of 25[OH]D levels between 20 to 40 ng/ml were quite small, levels higher than 20 ng/ml may not necessarily be beneficial. As the study was observational, clinical trials would be needed to ascertain the risks and benefits of vitamin D supplementation in adults with and without kidney disease.
Vitamin D deficiency is based on 25-Hydroxyvitamin D (25[OH]D) levels associated with rickets in children although there is currently no consensus on thresholds that define 25[OH]D deficiency or insufficiency. For example, the Institute of Medicine defines “risk of deficiency” as levels below 12 ng/ml and states that some, but not all, individuals may be at “risk of insufficiency” with 25[OH]D levels between 12 and 20 ng/ml (2). The Endocrine Society defines 25[OH] deficiency and insufficiency as levels below 20 ng/ml and levels between 20 and 29 ng/ml, respectively (3). The existing controversy over which 25[OH]D levels constitute “insufficiency” or “risk of insufficiency” and a supplementation requirement carries substantial public health relevance. This is because approximately half of the U.S. non-institutionalized adult population has a 25[OH]D level within the range 12 to 29.9 ng/ml (4).Thus, the majority of 25[OH]D supplementation is currently for treatment of “insufficient” rather than “deficient” levels of 25[OH]D. People who are confused about how much vitamin D they need should consult their doctor, the researchers commented.