Lead author Gregory Nichols, senior investigator with the Kaiser Permanente Center for Health Research in Portland, Ore., said heart attack and stroke risk increase when "good" cholesterol levels go down. Nichols and colleagues studied patients with diabetes because they are more prone to heart disease, with a lifetime risk as high as 87 percent.
While there is considerable evidence that reducing the amount of low-density lipoprotein, the "bad" cholesterol, can reduce the risk of heart disease, the relationship between HDL and heart disease is less clear, Nichols said.
The study involved 30,067 patients who entered Kaiser Permanente diabetes registries in Oregon, Washington and Georgia from 2001 to 2006. The patients had at least two HDL measurements between six and 24 months apart.
Sixty-one percent had no significant change in HDL levels. In 22 percent of patients, HDL levels increased by at least 6.5 milligrams per deciliter of blood; in 17 percent of patients, HDL levels decreased by at least that same amount.
The study, published in The American Journal of Cardiology, found patients whose HDL levels increased had 8 percent fewer heart attacks and strokes than patients whose HDL levels remained the same, while patients whose HDL levels decreased had 11 percent more heart attacks and strokes.
The researchers tracked the patients for as much as eight years.