The National Institutes of Health funded the trial, which recruited 25,871 healthy American men and women age 50 or older, including 5,106 African-Americans. Study participants were split into four groups and randomly assigned to take supplements or placebos, and they were followed for 5.3 years on average.
One group took 2,000 IUs (international units) of vitamin D3 and 1 gram of omega-3s every day. A second group was given vitamin D and a dummy pill in lieu of omega-3. A third group got omega-3s and a vitamin D placebo. And the final group received two placebos.
Pharmavite LLC of Northridge, Calif., donated the vitamin D agents and matching placebos, and Pronova BioPharma of Norway and BASF donated Omacor, a fish oil sold under the brand name Lovaza in the United States.
In many ways, the results are not surprising. The public has been barraged by a steady torrent of information about the health benefits of vitamin D in recent years, as studies have linked low levels of the vitamin to conditions as varied as diabetes, high blood pressure, cancer, heart disease and depression. Many primary care doctors now routinely test patients’ vitamin D levels and declare them deficient, and supplement sales have skyrocketed in recent years.
All along, however, critics have questioned whether vitamin D is merely a marker of overall health, and whether the threshold for deficiency was set too high. The so-called sunshine vitamin is synthesized in the body when skin is exposed to sunlight and is depleted by smoking, obesity, poor nutrition, and other factors. Certain foods, like fatty fish, eggs and fortified milk, also contain vitamin D.
The Institute of Medicine in 2011 concluded that most Americans get enough vitamin D and that deficiencies have been overstated. The group also noted that reports of potential benefits with higher blood levels have been inconsistent.