The breast cancer drug tamoxifen may also protect against heart disease, a study has found.
Tamoxifen has been shown to reduce the incidence of breast cancer in healthy women at high risk of developing the disease. However, the impact of the drug on heart disease has been the subject of much debate.
Some experts fear tamoxifen may increase the risk of heart disease as it can bring forward the menopause, after which women become more prone to developing heart problems.
Others believe the drug can reduce the risk of heart disease because it can help to reduce levels of harmful cholesterol in the blood.
The new research suggests it may have a beneficial impact on heart disease - but through a different mechanism.
Researchers discovered that women who took the drug had lower levels of two chemicals associated with inflammation - C-reactive protein (CRP) and fibrinogen - by 26% and 22% respectively.
High levels of both chemicals have been associated with an increased risk of cardiovascular disease in several studies.
Lead researcher Dr Mary Cushman, of the University of Vermont in Burlington, said: "Tamoxifen has mixed effects depending on the organ it is acting on.
Therefore, it is important to determine the drug's effects on other organs such as the heart and blood vessels, because cardiovascular disease is much more common than breast cancer."
Previous breast cancer trials have reported 15% to 60% reductions in cardiac death in women treated with tamoxifen.
In total, 111 healthy women, with an average age of 58, took part in the study. Every day for six months, 51 women took 20mg tamoxifen pills, and 60 took a placebo pill.
A spokesperson for the British Heart Foundation welcomed the research, but said more trials were needed.
She said: "This might be a bonus for women who are taking tamoxifen for breast cancer, but at this stage we would not recommend that tamoxifen is prescribed for women purely as a way to prevent cardiovascular disease."
Dr Kate Law, head of research at the Cancer Research Campaign, said: "This builds on good evidence that tamoxifen is not the long term risk that was first feared."
The research follows a study by a team in Pittsburgh, USA, published earlier this year which found no evidence that the drug posed an increased risk of heart disease.
A UK study is following 7,000 women taking tamoxifen as a preventative drug.
The study, which started seven years ago, will monitor breast cancer deaths and deaths from other causes.
There is some evidence that the drug does increase the risk of developing uterine cancer and cataracts.
The new research is published in Arteriosclerosis, Thrombosis, and Vascular Biology: Journal of the American Heart Association.