Breastfeeding protects against
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
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
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
Upon analyzing the data, adjusting for variables such age and cigarette
smoking, the researchers noted several interesting trends. One of the
strongest was a decreasing risk of RA with increasing duration for
breastfeeding. Looking at total lifetime breastfeeding, regardless of number
of children, women who had breast-fed for between 13 and 23 months had a 20
percent reduction in the risk of RA compared with women who did not
breastfeed. Women who had breast-fed for at least 24 months - two full years
out of their childbearing years - increased their risk reduction to 50
percent. "Our data suggest breast-feeding confers long lasting protection
against developing RA," Dr. Karlson states, "because the mean time since the
last pregnancy among women with RA was 25 years."
In addition, women who experienced irregular menstrual cycles between the
ages of 20 and 35 were shown to have an increased risk of subsequent RA.
Women who had begun menstruating at an early age, 10 or younger, were more
likely to develop seropositive RA. The study's results did not show any
association between a history of oral contraceptive use and disease risk, or
any significant differences in disease risk related to a woman's number of
Focusing on the sample of RA patients, compared to women who did not develop
RA, the researchers confirmed that the risk of RA increases with age and
demonstrated a peak risk at the typical time of menopause, age 50 to 54.
Because the onset of RA often coincides with menopause, some studies have
linked the disease to falling estrogen levels, indicating the potential
benefits of estrogen therapy. In this study, however, estrogen therapy among
postmenopausal women did not protect against RA.
"These findings suggest avenues for further research into the hormonal
mechanisms involved in RA, because the complex relationships between RA and
reproductive hormones clearly warrant further study," Dr. Karlson concludes.
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