Danish researchers said they have found the strongest evidence yet that an often ignored form of cholesterol can cause heart attacks.
They said people with higher levels of a little-understood form of cholesterol called lipoprotein (a), which varies up to a thousand fold from one person to another, were also more likely to have heart attacks.
Statins - taken by millions to cut heart attack and stroke risk - do not affect lipoprotein (a) but the findings may encourage the development of new cholesterol-lowering drugs, said Borge Nordestgaard of Copenhagen University Hospital, who led the study.
Risk more than doubled
The research, published in the Journal of the American Medical Association, showed that people with the highest lipoprotein (a) levels were two to three times more likely to have a heart attack than those with the lowest levels.
"We have shown that lipoprotein (a) is causing heart attacks," Nordestgaard said in a telephone interview.
Lipoprotein (a) is one of several forms of cholesterol found in the blood, with levels determined almost entirely by genetics.
Statins lower levels of low-density lipoprotein, commonly known as "bad" cholesterol. Top-selling statins include Pfizer's Lipitor, known chemically as atorvastatin, and AstraZeneca's Crestor, or rosuvastatin.
"This study may explain why statins don't work for some people," Nordestgaard said.
To show the role of lipoprotein (a) role in heart attacks, the Danish team analysed the genes of 45 000 men and women who gave blood samples for a large national survey starting in 1976, tested their lipoprotein (a) levels and then followed them until 2007.
People with the highest levels of this cholesterol had the most heart attacks, the study found. One certain genetic variation accounted for about a quarter of the cases of high lipoprotein (a).
"Lipoprotein (a) has been around for a long time as a risk factor but people hadn't taken it too seriously because they didn't think it caused heart attacks," Nordestgaard said. "Now we show that, like LDL, it is causing heart attacks."
One problem is that people have little control over the cholesterol, whose levels can vary up to a thousand-fold among individuals, Nordestgaard added.
Niacin, a vitamin often prescribed generically to lower cholesterol, also lowers lipoprotein (a) levels. It can cause uncomfortable flushing, however. Aspirin can also lower lipoprotein (a) levels.
Merck & Co markets a drug called Tredaptive in Europe that combines niacin with an anti-flushing agent but the drug has been rejected by US health regulators.
Nordestgaard said he hopes the study will spur drug makers to begin work on a new drug specifically aimed at lipoprotein (a) levels. – (Michael Kahn/Reuters Health, June 2009)
Heart disease – the risk factors