We all know our periods can be fickle friends, seemingly changing with the slightest gust of wind, bite (or 30) of milk chocolate, or whether or not you've been working out much lately. What you might not be prepared for, however, is how your period can change with the seasons - even if you've not made any overt changes to your routines.
If you feel like your menstrual cycle is affected by the seasons, you’re not wrong. This is because our cycles and hormones are easily influenced by external factors. Throw in the change of seasons and, without sugar-coating it, the sheer stress of being a human in this world right now, and it’s likely your period is pretty unpredictable at the moment. But don't throw your hands up in despair and cry I'll never understand my bloody body just yet, babe. Learning why these changes happen can not only make us more prepared to deal with our cycles but is the first step to learning how to harness and balance our hormones. If you're reading between the lines and wondering if this means you can actually change your cycle deliberately, then the answer is yes - to an extent (hey, there's always a disclaimer, right?)
Our menstrual cycles tend to be shorter in summer. Before you get the streamers and party poppers out and start extending your trips to the local lido (though, erm, maybe you shouldn't be doing that at all this year, for obvious reasons): they’re only shorter by less than a day, on average. However, if you are feeling the effects of the changes of the seasons on your cycle - whether your periods are noticeably shorter (and not by 90% of a day, thank you very much) or you're experiencing different PMS symptoms or side effects than you do at other times of the year, know that you’re not imagining it. In fact, there’s actual science to back it up (because god forbid we talked about our experiences in our bodies without existing scientific research backing up our claims!) The more drastic the weather change, such as flying to a tropical, sweltering hot country right after hanging out in sub-zero temperatures or living in a country with very extreme seasons, the more likely it is that the effects of this are felt.
In the U.K., while it can hardly be said that we're a country of extreme temperatures, we do tend to get very sudden, extreme heat waves that seemingly come out of nowhere and then vanish, leaving us fighting the impulse to turn the heating on in August (just me?)
The seasons affect our periods because, during summer, our bodies produce higher quantities of Follicle Stimulating Hormone (FSH), which increases our chances of ovulation, which is essentially the crucial step in the whole baby-making process our bodies seem so hell-bent on repeating, which subsequently shortens our cycles. FSH stimulates the follicles in your ovaries to grow and mature, and eventually release an egg ready to be fertilised (sexy, right?) at ovulation.
It’s been found that, in summer, there is a trend towards increased FSH secretion, larger ovarian follicle size, and a higher frequency of ovulation. Menstrual cycles were also found to decrease in length (the first day of your period to the last day before it starts again) by 0.9 days. Again, not ground breaking, but let's remember this is an average - for some people the change will be non-existent or minute, for others it might be noticeable even if you're not an obsessive cycle tracker.
The research concluded that it was increased sunshine, rather than temperature, which led to the cycle changes. During summer or in warmer, sunny climates, your body is producing more Vitamin D. Lower levels of vitamin D have been found to contribute to a longer follicular phase and a longer overall menstrual cycle; longer menstrual cycles are more likely to be anovulatory - meaning ovulation didn't occur. In winter, ovulation occurs and average of 71% of the time. In Summer, this percentage increased to a whopping 97%.
A quick tl,dr for anyone who, like me, gets a headache from too many statistics: if exposure to vitamin D increases our chances of ovulation, a lack of it in the winter months can lead to an anovulatory cycle, which tends to be longer.
The reason your menstrual cycle changes noticeably during summer (because, let's be real, that 0.9 day decrease in cycle length isn't keeping anyone up at night wracked with questions) could have more to do with the changes you’re making in other areas of your life that with the weather itself.
Lifestyle factors heavily affect our menstrual cycles and hormone production. One of the key reasons your period changes in summer could well be because you change - your habits, routines, sleep schedule, and even diet. Be honest, in summer you’re probably more likely to spend time outdoors, you’re likely eating much lighter meals than winter’s heavy, warming dishes, and incorporating more fresh fruits or seasonal veggies that differ from those available in colder months.
It’s also worth noting that weight changes can greatly impact your menstrual cycle, so if your seasonal dietary changes affect your weight or you’re actively ‘dieting’ during particular seasons, your menstrual cycle will feel the effects. Obligatory reminder that yo-yo dieting isn't doing your long-term health an favours and we recommend learning about your body and maintaining a well-balanced diet that adapts to the needs of your cycle, energy and activity levels, and lifestyle.
So let's talk stress. The stress hormone, cortisol, affects the hypothalamus, an area in the brain necessary for the regulation of hormones. When disrupted by cortisol, the signals it sends to the ovaries become scrambled, kinda like an out of tune radio, basically delaying or even entirely preventing ovulation from occurring. With mood easily and sometimes very-bloody-obviously impacted by the presence, or lack thereof, of sunlight - as sunlight also influences serotonin production in addition to that sweet sweet FSH-supporting vitamin D - it's not surprising that the knock-on effects of dramatic seasonal changes have big consequences for our cycles.
While it may not be as simple as 'summer = shorter periods', it is clear that summer, both due to the longer, brighter days it brings and the social and personal routine changes it inspires, definitely has an affect on our cycles.
If you're feeling thrown by the change of season - whether now or in a few months when the shorter, colder days creep back into our lives, you can learn to manage your cycle and harness your hormones through diet, exercise, and wellbeing practices.
Image credit: @haileybieber