CHICAGO — New research linking low vitamin D levels with deaths from heart disease and other causes bolsters mounting evidence about the “sunshine” vitamin’s role in good health.

Patients with the lowest blood levels of vitamin D were about two times more likely to die from any cause during the next eight years than those with the highest levels, the study found. The link with heart-related deaths was particularly strong in those with low vitamin D levels.

But megadoses of vitamin D pills can be dangerous and skin cancer risks from too much sunshine are well-known. Also, it can’t be determined from this type of study whether lack of vitamin D caused the deaths, or whether increasing vitamin D intake would make any difference.

Exactly how low vitamin D levels might contribute to heart problems and deaths from other illnesses is uncertain, although it is has been shown to help regulate the body’s disease-fighting immune system, he said.

It has been estimated that at least 50 percent of older adults worldwide have low vitamin D levels, and the problem is also thought to affect substantial numbers of younger people. Possible reasons include decreased outdoor activities, air pollution and, as people age, a decline in the skin’s ability to produce vitamin D from ultraviolet rays, the study authors said.

Some doctors believe overuse of sunscreen lotions has contributed, and say just 10 to 15 minutes daily in the sun without sunscreen is safe and enough to ensure adequate vitamin D, although there’s no consensus on that.