Taking oral contraceptives that contain oestrogen may decrease a woman鈥檚 risk of developing multiple sclerosis 鈥� at least in the short term.
Women who used birth control pills had a 40% lower risk of being diagnosed with MS for several years afterwards than those not taking the pills, found a study by 脕lvaro Alonso at Harvard School of Public Health, US, and colleagues.
Previous studies of the long-term likelihood of developing MS found no protective effect of oestrogen, says Alonso, but 鈥渙ur study had more precise information on the use of oral contraceptives, so it has been possible to see this short-term effect鈥�.
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Oestrogens influence immune responses and so may affect autoimmune diseases like multiple sclerosis, in which immune cells attack and destroy the insulating fatty layer around nerve cells that allows fast transmission of neural signals. Studies in mice have shown that oestrogens ameliorate a disease similar to MS.
Risks after birth
Alonso and colleagues compared data on 106 UK women who were diagnosed with MS between 1993 and 2000 with 1001 age-matched controls who had no signs of MS. These women鈥檚 anonymous medical records also indicated if and when they had taken oral contraceptives.
Alonso found that women who had taken contraceptives in the previous three years were 40% less likely to be diagnosed with MS than were those women who had not taken any oestrogen-based pills.
The researchers also found that women were more likely to be diagnosed with MS within six months after a pregnancy than they were at other times. This makes sense if increased oestrogen deters disease onset, the authors say, as the body鈥檚 oestrogen levels are particularly low after pregnancy.
Oestrogens in birth control pills are likely conferring only a short-term reduction in risk of MS diagnosis, Alonso says, because the previous work of some of his colleagues showed that contraceptives 鈥渄on鈥檛 change the risk of having the disease in the long term鈥�.
Low probability
If researchers can figure out exactly how oestrogen affects MS, they may gain insight into 鈥渨hat went wrong鈥� in the body that caused the disease to develop, says Rhonda R Voskuhl at the University of California, Los Angeles, US.
However, 鈥渘o one will want to take birth control pills to prevent themselves from getting MS,鈥� Voskuhl says, 鈥渂ecause the probability of getting MS is so low.鈥� About one in 1000 people in the western world will develop MS.
Alonso鈥檚 results are 鈥減romising, but we have to be careful,鈥� she adds. 鈥淐learly, what has to be done is a placebo-controlled trial: design it and do it and see what happens, as opposed to just looking back at records.鈥�
Journal reference: Archives of Neurology (vol 62, p 1362)
