Rheumatoid arthritis (RA), an inflammatory disease of the immune system, is between two and four times more likely to strike women than men.
Among women, RA is more likely to develop when reproductive hormonal levels are changing, such as in the first few months following a pregnancy and around the time of menopause. Although previous researchers have studied this topic, the relationship between hormones and the risk of developing RA remains unclear.
Seeking more conclusive evidence, a team of researchers led by Dr. Elizabeth Karlson at Brigham and Women's Hospital in Boston drew on a large sample – 121,700 women – to explore the contribution of hormonal factors occurring prior to the onset of RA and the impact of postmenopausal hormone replacement therapy on the risk of disease Their findings, published in the November 2004 issue of Arthritis & Rheumatism, strongly support the lasting benefits of breastfeeding in protecting against the disease. What's more, the researchers identified a new risk factor for RA: irregular menstrual cycles.
The study's subjects were all women enrolled in the Nurses' Health Study, a sweeping investigation of disease, health, and lifestyle, ongoing since 1976. Through extensive questionnaires, the research team documented each woman's reproductive history with attention to potential RA risk factors, including age at menarche, age at first birth, history of breastfeeding, use of oral contraceptives, and regularity of menstrual cycles and in older women studied the use of estrogen after menopause. Among these women, the researchers confirmed 674 RA patients, diagnosed anywhere between 1976 and 2002. Most of the women were middle-aged at disease onset; the mean age was 56 years.