Hormone Replacement Therapy Reduces Bad Cholesterol, Lipoprotein (a)

Lp (a) is a fat cousin to low-density lipoprotein, or LDL, the "bad" form of cholesterol. Lp (a) can increase the risk of heart attacks and strokes by carrying cholesterol to the blood vessels, where it forms blood vessel obstructions. Lp (a) is also "prothrombotic" -- it stimulates unwanted blood clotting, which can block blood flow to the heart or brain.

"Elevated Lp (a) is considered to be 'a substantial risk factor,'" says Mark Espeland, Ph.D., professor of the section on biostatistics, Bowman Gray School of Medicine, Winston-Salem, N.C. So just as with LDL, it's important to have low blood levels of Lp (a).

Women in the study were enrolled in the Postmenopausal Estrogen/Progestin Intervention investigation, designed to assess the effect of these hormones on risk factors for heart attack and stroke. The three-year study, the largest randomized trial to look at Lp (a) and estrogen, included 366 women, 45 to 65 years old, who were given estrogen alone or with one of two different progestins. Progestins were added to estrogen to minimize the risk of endometrial cancer from estrogen alone.

Two groups received the drug medroxyprogesterone acetate (MPA), with group one taking a continual dose and the other group taking the drug for 12 days at high concentrations. A third group received micronized progesterone, a newer form of progestin. At one year estrogen therapy alone resulted in a 25.8 percent drop of Lp (a) compared to placebo. At 36 months the drop was 20.4 percent. Women taking MPA at a continual dose had reductions in Lp (a) of 27 percent at 12 and 36 months. For women taking the drug at a 12-day high dose, there was a 23 percent decrease at both time points. The corresponding reductions in Lp (a) were 16 and 26 percent for women taking micronized progesterone.

"The study confirms that hormone therapy has a broad-scale and sustained impact on cholesterol metabolism," says Espeland. "And we found that the results were the same, regardless of a woman's age, weight or prior hormone use."

In 1995 the researchers reported that estrogen therapy alone resulted in increased levels of the "good" cholesterol, high-density lipoprotein, HDL. "This report extends these analysis to Lp (a) concentrations," says Espeland.

Co-authors are Santica Marcovina, Ph.D., Sc.D; Valery Miller, M.D.; Peter Wood, D.Sc.; Carol Wasilauskas, M.D.; Roger Sherwin, M.B., B.Chir.; Helmut Schrott, M.D.; and Trudy Bush, Ph.D.