Nursing lowers rheumatoid arthritis risk

Moms whose breastfeeding totals 24 months are only half as likely to develop the disease as other women, researchers found

The Globe and Mail 
Thursday, November 4, 2004

The longer a woman breastfeeds her children, the lower her risk of developing rheumatoid arthritis later in life, according to a new study.

Women who breastfeed for a total of 24 months see their risk plummet by half, researchers found. And even those who fed their babies naturally for as little as 12 months still saw the risk decline by 20 per cent.

The research, published in today’s edition of the medical journal Arthritis & Rheumatism, also found that women with irregular menstrual periods and those who start menstruating at an early age (10 or younger) have a greater risk of developing rheumatoid arthritis.

The study did not find a link between the use of oral contraceptives or hormone-replacement therapy and rheumatoid arthritis.

There is a lot of evidence linking sex hormones to rheumatoid arthritis, a debilitating autoimmune disease. (It is not to be confused with osteoarthritis, a more common form of joint pain.) But this is the first study to look at a range of reproductive factors.

Rheumatoid arthritis afflicts far more women than men; it usually strikes around the time of menopause, or the months just after pregnancy.

Dr. Elizabeth Karlson of the Harvard School of Public Health and the lead researcher said it is believed that a woman’s risk of developing rheumatoid arthritis grows as levels of the female sex hormones estrogen and progesterone fall.

She said that while the benefits of breastfeeding are clear in the new study, the biological mechanisms remain murky. Levels of progesterone and estradiol (a form of estrogen) soar during pregnancy but fall sharply in the postpartum period.

"We hypothesized that breastfeeding would increase the risk of rheumatoid arthritis," Dr. Karlson said. "However, our findings demonstrated the opposite."

Similarly, researchers thought women who took hormone-replacement therapy (a pill that usually combines estrogen and progesterone) would lessen their risk of developing rheumatoid arthritis, but they found no such link.

Dr. Karlson said this leads her to believe that other factors are at play. In particular, she believes that other hormones such as prolactin and cortisol -- whose production increases sharply when a woman breastfeeds -- may play a role in preventing rheumatoid arthritis.

"The complex relationship between RA and reproductive hormones clearly warrants further study," she said.

Data were derived from the Nurses' Health Study, a massive research project that has been ongoing since 1976. Of the 121,700 participants, 674 were confirmed to have developed rheumatoid arthritis. On average, the disease was detected 25 years after their last pregnancy -- at a median age of 56. But among women who breastfed their children, the risk of rheumatoid arthritis fell sharply, and when they did develop the condition, the onset came much later.

Analysis of the data showed that the number of children a woman had and the age at which she gave birth did not appear to make a difference, but the cumulative time she spent breastfeeding did.

"This suggests that breastfeeding confers long-lasting protection against developing RA," Dr. Karlson said.

Women who described their menstrual periods as "very irregular" from ages 20 to 35 saw their risk of developing rheumatoid arthritis increase by about 40 per cent, while those who experienced menarche (first menstruation) before age 10 had a risk that was 60-per-cent higher.

One in seven Canadians, about four million people, suffer from one or more of the more than 100 conditions that constitute the inflammatory joint diseases known as arthritis. These include osteoarthritis, rheumatoid arthritis, gout, lupus and fibromyalgia. For every two men who have rheumatoid arthritis, there are five women.

Most of the research on breastfeeding has focused on the impact on children who are breastfed, not on their mothers.

Previous studies have shown that children who are breastfed have a lower risk of developing high blood pressure, obesity, insulin resistance (a precursor to diabetes) and cardiovascular disease.

The biological mechanism is not entirely clear, but all these conditions are linked to a person’s metabolism and, more specifically, to the body’s inflammatory (or immune) response.

Rheumatoid arthritis is also a result of dysfunction in the body’s inflammatory response.