Birth control pills are one of the most popular ways American women prevent pregnancy, but scientists still don’t fully understand the medication’s unintended side effects. Now, a study points to a newly detected side effect of birth control: physical changes to a crucial area of the brain.
Brain scans from 50 women show that oral contraceptive pills may impact brain structure — something that previous studies haven’t really looked into, Michael Lipton, a professor at Albert Einstein College of Medicine and the study’s lead author, tells Inverse.
Lipton and his team determined that oral contraceptive pills, or OCPs, were linked to lower brain volume in the hypothalamus. This is the area of the brain that affects body processes, like body temperature and heart rate, and brain processes, like appetite, mood, and sex drive. The new findings add an extra dimension to these known side effects.
The preliminary study was presented this week at the annual meeting of the Radiological Society of North America.
How birth control changes the brain
Birth control pills could physically alter the hypothalamus, but that may not actually be a bad thing.
Lower hypothalamic volume is linked to experiencing less anger and depression symptoms, according to the new results. But Lipton tells Inverse that he’s still not sure how these changes in the brain really play out.
There were significant differences in the hypothalamic volume between the 29 women in this study who took hormonal birth control pills and the 21 who did not. The results don’t prove that birth control pills directly caused those changes to happen.
“We do not yet know that the effect is definitely a cause of [the pills] or that there are any adverse effects,” Lipton says.
As for the mood effects, the slight decrease in anger and depressive symptoms that accompanied the smaller hypothalamic volume is surprising.
Past research suggests that birth control pills are associated with an increase in depression traits. The study doesn’t contradict those findings, but it does give a more detailed look at how brains on birth control change.
Birth control and brain volume
The idea that brain volume changes when a person is on birth control isn’t as far-fetched as it may seem. Scientists already know that sex hormones like estrogen and progesterone can cross the blood-brain barrier, and when hormones fluctuate naturally they do affect the brain, Lipton says.
Meanwhile, hormonal variation during the average menstrual cycle is linked to structural and functional brain changes. Taking an oral pill may also have similar affects on the brain, the study suggests.
The pill was approved by the US Food and Drug Administration in 1960, but the fact that these pills are linked to measurable changes in brain volume, is new, Lipton says.
The results demonstrate the power that sex hormones hold over the body — even in places that we may not expect, Lipton says. Though this research is preliminary, birth control pills have been taken by millions of women every day for nearly six decades. It’s high time scientists learned exactly what happens when they take it.
Method and Materials: We acquired high-resolution MR images of the brain at 3T for a prospective cohort of 50 healthy women. Psychometric tests (Cogstate and PROMIS) were administered at the time of imaging. 21 participants took OCPs at the time of imaging while 29 did not. After training and validation, 5 raters independently performed manual segmentation of the hypothalamus using ITK-SNAP. Total intracranial volume (tICV) was determined using FreeSurfer. The intraclass correlation was calculated for a subset of 20 randomly selected cases to assess inter-rater reliability. A general linear model was fit to test for the association of OCP use with hypothalamic volume, with tICV and birth control used as covariates. Additional exploratory analyses assessed associations with menstrual cycle phase and with cognitive and health measures.
Results: The inter-rater ICC was 0.86. Total hypothalamic volume in participants taking OCPs was smaller than those not taking OCPs (b=-63.4 ± 22.2, p=0.006). There was a significant association of hypothalamic volume with greater anger (p=0.02) as well as a strong correlation with depression (p=0.09). However, no significant correlation was found between hypothalamic volume and cognitive testing results.
Conclusion: Our hypothalamic segmentation method is highly reliable. OCP use is associated with smaller total hypothalamic volume, which may be related to interference with known trophic effects of sex hormones and provide a structural mechanism for OCP-mediateed inhibition of folliculogenesis as well as potential functional effects.