The largest brain imaging study of a woman to date shows that hormonal birth control can decrease brain volume 鈥� though it isn鈥檛 clear what effect, if any, this has on brain function.
Hormonal contraceptives have been around since the 1960s. Yet scientists only began investigating their potential effects on the brain in the past decade or two, says at the University of Minnesota. Previous studies have shown between women who take hormonal contraceptives and those who don鈥檛. But no one had studied the brain before, during and after taking hormonal birth control.
Heller, who was 30 years old at the time the study began, had previously used hormonal birth control once for 12 years but had stopped taking it about five years before the study.
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The researchers scanned Heller鈥檚 brain using magnetic resonance imaging (MRI) five times a week, at the same time each day, for five weeks while she wasn鈥檛 using birth control. She then started taking birth control pills that contained synthetic forms of both oestrogen and progesterone 鈥� one of the most popular forms of contraception in many countries including the US and the UK. Three months later, Heller underwent 25 more brain scans across five weeks. She then stopped using the oral contraceptive and, three months later, repeated the scanning procedure for a final five weeks, marking 75 total brain scans.
As part of the study, Heller measured her body temperature and provided a blood sample before each scan to determine what phase of her menstrual cycle she was in. She also completed daily psychological questionnaires to track her mood and anxiety levels and logged her sleep, and how much water, alcohol and caffeine she drank each day. Heller tried to keep her physical activity and diet consistent throughout the study as well 鈥� one of the benefits of being your own study participant, she says.
The collection of brain scans created a detailed picture of how Heller鈥檚 brain changed across both her natural menstrual cycle and with hormonal contraception. However, the researchers didn鈥檛 capture her full menstrual cycle in the first 25 scans. 鈥淚 had a prolonged cycle then,鈥� says Heller, who presented these findings on 7 October at a Society for Neuroscience meeting in Chicago. So, they didn鈥檛 include them in their preliminary analysis.
The researchers found the volume of Heller鈥檚 cerebral cortex 鈥� the brain鈥檚 outermost layer 鈥� was 1 per cent lower while she was on birth control compared with when she stopped the medication. This is in line with previous studies that have indicated hormonal birth control may decrease volume in certain areas of the cortex.
Heller says a decrease in cortical volume isn鈥檛 necessarily a bad thing. For instance, it also occurs during puberty and pregnancy when the brain refines neural pathways to make them more efficient. 鈥淭his could be [happening] for the brain on oral contraceptives,鈥� says Heller. 鈥淏ut for now, we don鈥檛 know what this means, and that鈥檚 why it鈥檚 so important that we do more research on the topic.鈥�
It is also essential to remember that hormonal birth control affects people differently. Just because Heller experienced decreases in cortical volume doesn鈥檛 mean everyone will, she says. 鈥淵ou cannot generalise these findings to a larger population.鈥�
Still, the work is聽a crucial step towards understanding why some people experience negative side effects, such as depression, on hormonal contraceptives while others don鈥檛, says at the University of Michigan.
