People sunbathed in Paris in August as an unusual heatwave continues to hit continental Europe. (Photo: Reuters)

Low levels of vitamin D are being linked to a long life, according to a new study, calling into question previous research that said the so-called "sunshine vitamin" could help prevent heart disease, diabetes, cancer, allergies and mental illness.

"We found that familial longevity was associated with lower levels of vitamin D and a lower frequency of allelic variation in the CYP2R1 gene, which was associated with higher levels of vitamin D," wrote Dr. Diana van Heemst, Department of Gerontology and Geriatrics, Leiden University Medical Center, Leiden, the Netherlands, with coauthors.

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Now scientists and physicians are questioning the previous belief that human beings require a certain amount of sun exposure for optimal health. In 2008, a well-regarded study came out stating that people with low vitamin D levels had more than double the risk of dying from heart disease and other causes over an eight-year period compared with those with the higher vitamin D levels.

At the time, the government's dietary recommendations were 200 IUs a day up to age 50, 400 IUs to age 70, and 600 IUs over 70. But physicians thought those numbers were way too low, and instead suggested supplementing 2,000 IUs per day plus daily sunshine. 

In addition to preventing heart disease, they believed the vitamin could help ward off osteoporosis, breast cancer, prostate cancer, colon cancer, depression and insomnia. The new information is causing doctors and patients to rethink sun exposure all over again - especially given skin-cancer risks.  

The authors of the study, led by Dr Diana van Heemst, explained: "We found that the offspring of nonagenarians who had at least one nonagenarian sibling had lower levels of vitamin D than controls, independent of possible confounding factors and SNPs associated with vitamin D levels." 

The study, which consisted of date from 380 families with members who survived into their 90s, measured levels of 25(OH) vitamin D as they varied from month to month. A total of 1,038 offspring of the elderly siblings were also included. The findings were reported in the Canadian Medical Association Journal.