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Do birth control pills block muscle gains in women?

According to a study just presented at the annual Experimental Biology 2009 conference in New Orleans, women who use oral contraceptives, better known as birth control pills, may experienced hampered muscle gains when they lift weights. The study consisted of 73 healthy women, ages 18 to 31, who were assigned to either a birth control pill group (BCP), or a non-birth control group (NBCG). All the women participated in a 10-week weight-training program, training 3 days a week under the supervision of physiologists. They did both standard upper and lower body exercises, all for 3 sets of 6-10 reps, using weights equal to 75% of their maximum one-rep lift. Body composition in the women was measured by hydrostatic weighing. In addition, blood samples were obtained prior to, and after the training to measure various hormones, including DHEA, DHEA-S,  and IGF-1.

The results showed that those not taking BCP gained 60% more lean mass compared to those taking the pills. On the other hand, strength gains and arm and leg circumferences were similar between the groups. The levels of the anabolic hormones, DHEA and IGF-1, were significantly lower in the women on the pill, while levels of the catabolic hormone, cortisol were higher in the pill users. The OCP also showed decreased levels of DHEA at the end of the study. In contrast, no change occurred in DHEA levels in the non-pill users.

The researchers who conducted this study were at a loss to explain the results, other than suggesting that BCP can impede muscle gains in women. On the other hand, while the pill users gained 60% less lean mass compared to their non-pill peers, both groups gained similar levels of strength and size in the legs and arms. This, of course, is a quite contradictory finding, and makes you wonder if much of the lean mass gains experienced by the non-pill users consisted of water. Curiously, testosterone wasn’t measured in the study, which would have somewhat clarified the results. Instead, only DHEA levels were measured. DHEA, however, is an adrenal androgen that tends to convert into testosterone in women far more readily that it does in men. But recent studies also show that DHEA doesn’t appear to promote muscle gains in exercising women. Since the women trained under supervision, we have to assume that they trained with an equal level of intensity, which would have influenced muscle gains. The elevated cortisol levels in the pill users likely played a major role in why they gained less lean mass, since the non-pill users didn’t show such elevations. The women were told to ingest at least 0.5 grams of protein per pound of bodyweight. Normally, a high protein intake would offset much of the muscle catabolic effects linked to higher cortisol levels, but this level of protein may not have been enough to overcome the catabolic effects probably induced by the OC.

This new information does not apply to women using anabolic steroid drugs, which would make any effects of OC on muscle growth negligible. As the study authors suggest, there may be other, as yet unidentified mechanisms as work here, too. In the meantime, I doubt that many women would be willing to toss those birth control pills as a means of promoting muscle gains. Becoming pregnant when you don’t want to is a far more serious proposition than sacrificing some muscle gains in rational women.

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