The immune system also gets "its period"

Do you know this too?

It’s cycle day 10 - just before ovulation - and you're sitting in a bus full of people coughing and sniffling. Nothing happens to you. Your immune system can handle any virus. Waiting for your period to arrive any day, on the other hand, things look very different. Every cold seems to jump out at you. If it goes particularly badly, you have period pains, fever, and sore throat at the same time. Wonderful!

In fact, this constellation is anything but rare. And that, say scientists, is no coincidence. Over the past 20 years, numerous studies have shown that the immune system is actually less active in the second half of the cycle. In the luteal phase - the time between ovulation and the start of menstruation - the immune response to pathogens is milder. Nothing should endanger the implantation of the embryo.

An exciting relationship: sex hormones and immune defense

The interaction of hormones and a woman's immune defenses has not yet been conclusively researched. What is already known is the effect of high estrogen levels in the first phase of the cycle, the follicular phase. Estrogen interacts with immune cells (among other things) by docking with receptors on the outside of these cells and by interacting with cellular processes on the inside. This results in inflammatory responses and defense against potential pathogens1. Girls and women have - statistically, exceptions prove the rule - a stronger immune system than men and boys. In the first half of the cycle, the differences are thus particularly great. Unfortunately, females are also more prone to autoimmune diseases, an undesirable effect of the grandiose immune response2,3.

Then, just in time for ovulation, the estrogen level drops and at the same time the progesterone level rises. Testosterone also has an influence during this phase, but exactly what that is is still being researched. In any case, these processes gently suppress the immune system in a strong enough way that many women with autoimmune diseases feel better than before, and so severely that a fertilized egg cell cannot be misinterpreted as a pathogen and attacked. Unfortunately, this is also how many a cold or diarrhea virus gets to its target2.

During the second phase of the cycle, the luteal phase, estrogen and progesterone rise together. Shortly before the time when you are waiting for your period (if you do not want to become pregnant), the levels of both estrogen and progesterone drop sharply again. This drastically lowers your immune defense for a short time. Good if you have just conceived a baby. Less good if you are not expecting a child and are sitting on the bus or train full of sniffling contemporaries2.

What remains to be researched

Unfortunately, no study results are yet available that allow conclusions to be drawn about when girls and women should ideally get vaccinated. It would be interesting to learn whether the immune response and/or vaccination reactions differ depending on whether the shot was given in the luteal or follicular phase.

Research is also still needed into the effect of hormonal contraception on the immune response. Contraception affects the immune response as the "pill" contains artificial hormones. Do permanently elevated levels of sex hormones mean fewer infections? Or, on the contrary, are there more of them? There are indications that some pills containing only progestin, an artificial progesterone, throttles inflammatory responses in the body in such a way that the tendency towards infection increases1. Here, too, however, many questions remain unanswered.

In all phases of the cycle, it makes sense to strengthen your immune system - for example, by eating a diet rich in vitamins and minerals, getting plenty of fresh air and exercise, and getting enough sleep. But research on the cycle-dependent nature of the immune system suggests that on some days it's even more important to take good care of yourself and perhaps to be extra meticulous with the fit of your mouth-nose protection, spacing, and hand hygiene.

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1.   Alvergne A, Tabor VH: Is Female Health Cyclical? Evolutionary Perspectives on Menstruation. arXiv preprint arXiv:1704.08590. 2017 Apr 26.

2.     Maegan Boutot: The immune system and the menstrual cycle, Helloclue 2018.

3.     Oertelt-Prigione S. Immunology and the menstrual cycle. Autoimmunity reviews. 2012 May 31;11(6):A486-92,

4.     Cunningham M, Gilkeson G. Estrogen receptors in immunity and autoimmunity. Clinical reviews in allergy & immunology. 2011 Feb 1;40(1):66-73.