Among seniors with a high risk of bone fractures, taking vitamin D or calcium pills has no impact on their chances of dying from cancer or vascular disease, researchers say in a new study.
Vitamin D is considered beneficial for bone health, and earlier studies have found that having low vitamin D levels in the blood is tied to a greater chance of dying from heart problems.
The thinking, therefore, has been that taking extra vitamin D might cut that risk.
"There's a lot of interest in vitamin D preventing heart disease and cancer, but the evidence from randomized trials is weak," said Dr. Alison Avenell, the lead author of the study and a researcher at the University of Aberdeen in England.
In the latest study, published in the Journal of Clinical Endocrinology and Metabolism, the researchers tracked the health of nearly 5,300 people over age 70 who had had a bone fracture.
The participants were randomly divided into four groups: one took 800 IU (International Units) of vitamin D daily, the second group took 1000 milligrams of calcium each day, a third group took both supplements, and a fourth group took fake pills that looked like the supplements.
People in the study took the pills for two to five years, and were followed for up to three years afterward.
Among people who took vitamin D, 32 out of every 100 died during the study, while 33 out of every 100 people who did not get the supplement died. That small difference could easily have been due to chance, the researchers found.
There were no differences in deaths from cancer or heart disease either. Calcium also proved unhelpful.
A recent analysis of 50 studies on vitamin D and heart health found no impact from taking the vitamin.
Still, Avenell said her study doesn't provide the final answer on whether vitamin D can help stop heart disease or cancer.
"People often stopped taking their tablets, so we might not have had enough people taking tablets to find effects," Avenell wrote in an email to Reuters Health. "The dose of vitamin D might not have been high enough."
Peggy Cawthon, a researcher with the California Pacific Medical Center Research Institute who was not involved in the new work, said people should be cautious regarding information on vitamin D's alleged heart and cancer benefits.
"A supplement or vitamin might not have the magic bullet to prevent the next disease," Cawthon told Reuters Health. "We've had a lot of examples, and vitamin D is just the latest showing it has no effect on these health issues."
Vitamin D is formed in the skin when it is exposed to sunlight. Though higher levels of the molecule are linked to better heart health, it could be that the vitamin D is only a sign of general health, and not something that actually improves the heart's function.
"My thought is that people who are healthier get out more and would produce more vitamin D," speculated Cawthon.
Avenell said she is looking forward to two other studies in the Unites States and the UK that will help confirm whether vitamin D has benefits beyond boosting bone strength.