Overdose is useless

Vitamin D did not reduce the risk of fractures in adults

Slava Gomenyuk, N+1

A randomized five-year study involving almost 26 thousand people showed that taking two thousand international units of vitamin D3 daily does not reduce the risk of fractures in healthy American adults compared with taking a placebo. As reported in an article published in The New England Journal of Medicine (LeBoff et al., Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults), adjusted for age, gender, race, body mass index and serum 25-hydroxyvitamin D concentrations, the risk difference between the groups remained statistically insignificant.Of all the variety of effects of vitamin D, doctors are more often interested in its effects on the skeletal system, since it maintains a sufficient level of calcium in the blood, which is necessary for bone mineralization. In addition, vitamin D receptors were found in the bones themselves, the activation of which was associated with the development of osteoblasts and the formation of bone tissue. A decrease in bone mineralization leads to osteoporosis — a violation of the architectonics of bone tissue and a decrease in its density, which ultimately leads to bone fragility and pathological fractures in adulthood.

Since such fractures are a big public health problem (for example, two million osteoporotic fractures are registered annually in the USA, about 600 thousand in Russia), the issue of their prevention worries doctors around the world. In 2011, the US National Academy of Medicine established recommended prophylactic doses of vitamin D for adults in the amount of 600 to 800 international units per day, which meet the body's needs for bone health for 97.5 percent of the population. In Russia, endocrinologists recommend taking from 800 to 1000 international units of vitamin. However, it is not completely clear how well such supplements reduce the risk of fractures. The results of randomized trials have shown both their benefits and uselessness, and sometimes even harm.

Meryl LeBoff and colleagues from Harvard Medical School used data from the VITAL study, which was devoted to the effect of taking two thousand international units of vitamin D and/or one gram of omega-3 unsaturated fatty acids on the risk of cardiovascular and oncological diseases in American adults. In total, 25,871 healthy people (men over 50 years old, women over 55 years old) were included in the new study, who were equally divided into those who took two thousand international units of vitamin D daily and those who took a placebo. The average age of the participants was 67.1±7.1 years. There were equal numbers of men and women, and 20.2 percent of the participants were black.

Participants agreed to limit any additional (not included in the study) vitamin D supplements to 800 international units per day and calcium to 1200 milligrams per day. Adherence to drugs (vitamin and placebo) was 87.3 percent after two years and 85.4 percent after five years. Participants reported fractures in annual reports and provided medical documents. On average, the participants were followed for 5.3 years.

A total of 1,551 participants had a 1991 fracture (769 out of 12,927 participants in the vitamin D group and 782 out of 12,944 participants in the placebo group). Additional intake of two thousand international units of vitamin D3 did not significantly affect the total number of fractures compared with placebo (risk ratio 0.98; p=0.70). The researchers also found no significant reduction in the number of fractures that do not affect the spine (in 721 participants in the vitamin D group and 744 in the placebo group; risk ratio 0.97; p=0.50) or hip fractures (in 57 participants in the vitamin D group and 56 in the placebo group; risk ratio 1.01; p=0.96) adjusted for age, gender, race and intake of fatty acids.

Baseline data (age, gender, race, body mass index and taking additional doses of calcium or vitamin D) did not significantly affect the results of the study. Baseline levels of 25-hydroxyvitamin D in the blood serum of the participants also did not change the likelihood of fractures of all three types.

Also, serum calcium levels (measured in 15,884 participants) and parathyroid hormone levels (measured in 16,803 participants) did not affect the frequency of fractures. The researchers found no significant differences in the frequency of fractures among participants who took medications for osteoporosis. As for adverse reactions, there were no significant differences in the frequency of increased calcium content in the blood and the formation of kidney stones between the groups.

This study shows that daily intake of an additional two thousand international units of vitamin D3 does not reduce the risk of fractures in healthy adult men and women compared with placebo. The difference between the groups remained insignificant even when adjusted for age, gender, race, serum 25-hydroxyvitamin D concentration and other indicators.

In general, vitamin D has been having a hard time lately: increasingly, scientists are discovering its uselessness in some conditions. Recently we told that it did not help in the prevention of diabetes, respiratory infections and depression.

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