The National Institutes of Health funded the trial, which recruited 25,881 healthy American men and women aged 50 or older, including 5,106 African-Americans. Study participants were divided into four groups and randomly assigned to take supplements or placebo, and they were followed for 5.3 years on average.
One group consumed 2,000 IU (international units) of vitamin D3 and 1 gram of omega-3 every day. The second group was given vitamin D and dummy pills as a substitute for omega-3. The third group received omega-3 and placebo vitamin D. And the last group received two placebos.
Pharmavite LLC from Northridge, California, donated suitable vitamin D and placebo agents, and Pronova BioPharma from Norway and BASF donated Omacor, fish oil sold under the Lovaza brand in the United States.
The results, published in The New England Journal of Medicine, are being presented Saturday at the American Heart Association conference in Chicago.
In many ways, the results are not surprising. The public has been flooded with a continuous flow of information about the health benefits of vitamin D in recent years, because research has linked low levels of vitamins to conditions as diverse as diabetes, high blood pressure, cancer, heart disease and depression. Many primary care doctors are now routinely testing patients' vitamin D levels and claiming they are deficient, and increasing sales have skyrocketed in recent years.
Nonetheless, critics question whether vitamin D is only a marker of overall health, and whether the deficiency threshold is too high. The so-called sunshine vitamins are synthesized in the body when the skin is exposed to sunlight and run out by cigarettes, obesity, malnutrition and other factors. Certain foods, such as 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 deficiency has been exaggerated. The group also noted that reports of potential benefits with higher blood levels were inconsistent.