About 869,000 Americans die of heart disease each year, according to the American Heart Assn.
"They certainly have made the link between diabetes and cardiovascular disease," said Dr. Mason Weiss, a cardiologist at Centinela Hospital Medical Center in Inglewood, who was not involved in the study. "Now the research must be on what the mechanism is."
Giovannucci speculated that several mechanisms could be responsible. Previous studies have suggested, for example, that low vitamin D levels lead to a buildup of calcium in atherosclerotic plaques on the walls of arteries, increasing the risk of heart attacks.
It could also affect blood pressure, or even have a direct effect on functioning of heart muscles, making them more susceptible to arrhythmias.
"We obviously need to understand the mechanism better," he said. "But that requires randomized trials, which is a big undertaking."
Weiss joined the growing chorus of researchers calling for changes in federal guidelines to reflect the new data.
"The next time they review the daily requirements, they should look at all these articles," he said.
Increasing the recommended intake of vitamin D "could have a significant health benefit" and would be a cost-effective change.
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thomas.maugh@latimes.com
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(BEGIN TEXT OF INFOBOX)
The sunshine vitamin
A growing body of evidence suggests that people who are deficient in vitamin D have higher risks of cancer, diabetes, autoimmune diseases and, according to the most recent study, heart attacks. Here's what you need to know:
Levels
* Current recommendations call for an intake of 400 IUs, or international units, for most people, twice that for the elderly.
* Recommended blood levels are about 30 nanograms per milliliter.
* Many researchers recommend consuming 1,500 to 2,000 IUs per day and attaining blood levels of 50 to 60 nanograms per milliliter.
Sources
* Ultraviolet B in sunlight converts natural precursors in the body into vitamin D. Sunbathing at noon in summer produces 20,000 IUs in 20 minutes in Caucasians. Additional exposure simply damages the skin. Darker-skinned people require three to five times as much exposure to produce the same amount. Sunblock interferes with production.
* The primary dietary source is oily fish and fortified milk, margarine and fortified cereal. Fish has about 350 IUs per serving. Milk contains about 100 IUs per glass, and margarine has about 60 IUs per tablespoon.
Source: Times research
