It is well known that high-density lipoproteins (HDL) protect against heart disease while low-density lipoproteins (LDL) promote it. However, recent research has shown that the relationship is not that simple. The effectiveness of both types of lipoprotein change when they are oxidised by free radicals highly reactive by-products of metabolism. If LDL becomes oxidised its ability to cause heart disease increases. If HDL becomes oxidised its ability to protect against heart disease is lessened.
Researchers from St. Michael's Hospital, part of the University of Toronto, have shown that estrogens can act as antioxidants, which neutralise free radicals, and hence protect HDL from oxidation. In addition, high levels of HDL are able to protect LDL from oxidation, and this ability is strongly enhanced when estrogens are present.
Dr Bhagu Bhavnani's team, who carried out the research, write, "The inhibition of HDL oxidation and the enhancement provided by estrogens toward the inhibition of LDL oxidation may be another way in which estrogens reduce the risk of coronary heart disease in healthy young postmenopausal women."
Although recent randomised control trials have shown that HRT in older women may not reduce the incidence of coronary heart disease, Dr. Bhavnani believes that this is not the whole story. Although his team carried out experiments in test tubes rather than in human subjects they saw that estrogen had beneficial effects at concentrations lower than those found in women on HRT. He urges that, "randomised control trials using lower doses of HRT, different estrogens and progestins, and in younger postmenopausal women, from 50
Contact: Gemma Bradley