Why is a woman's heart stronger than a man's

Female sex hormones protect the heart from problems associated with disturbances in circadian rhythms

Kirill Stasevich, "Science and Life"

It is known that heart problems in women begin on average later than in men. The first thought that suggests itself here is that it's all about female sex hormones, which affect not only the reproductive system, but also the entire body as a whole. However, as researchers from the University of Guelph write in Cardiovascular Research, it's not just about hormones, but also about circadian rhythms.

Earlier, Tami Martino and her colleagues in experiments on mice showed that in male individuals, the consequences of a heart attack are much more severe if the attack occurred during sleep. Any phenomenon that depends on the time of day is related to the biological clock. 

To understand what the biological clock has to do with it, the authors of the work introduced mutations in the clock gene – one of the main genes that control circadian rhythms. The protein encoded by clock includes the gene of another protein – per, which is considered to be the "clock spring" of circadian rhythms (recall that this year they were given for deciphering the mechanism of operation of per Nobel Prize in Physiology or Medicine).

A mutation in the clock gene leads to a breakdown of the internal clock – figuratively speaking, its "spring" continues to contract and unclench, but without any clear rhythm. And it turned out that for a male heart, a spoiled biological clock is more dangerous than for a female one: with age, male mice who had a mutation in clock had heart diseases more often than females with exactly the same mutation.

Moreover, it was found out that males and females have different heart cells. Glucose metabolism and energy metabolism in general were disrupted in the male heart – obviously, the problems began because the heart could not provide itself with energy in due measure. At the same time, a special kind of cardiolipins appeared in the heart cells of males, which are characteristic of a sick heart. 

Cardiolipins are called lipids, which are found in abundance in the membranes of mitochondria – cellular organelles engaged in the production of metabolic energy. The reactions in which energy is extracted occur just on mitochondrial membranes, and the efficiency of mitochondria strongly depends on what they have with the membranes. Therefore, it is not surprising that changes in the composition of cardiolipins can affect the condition of the whole heart.

As for the females, despite the mutation in the "clock" gene, their cardiolipins were healthy, and everything was more or less in order with the metabolism.

But what does it have to do with hormones, which we talked about at the very beginning? It turned out that when the ovaries were removed from the females with the clock mutation, their hearts began to deteriorate as quickly as in males. That is, female sex hormones synthesized in the ovary somehow protect the heart, even when problems begin in the biological clock. 

With regard to people, we can say that with age, most likely, both men and women equally upset their biological rhythms, but women have an additional hormonal fuse in such a case, but the male heart remains defenseless.

In the future, it will be necessary to find out exactly how the "clock" defects affect the lipid composition of heart cells, and which female sex hormones help to soften the breakdown in the circadian rhythm, and how they do it, and whether it is possible to use female sex hormones (or their analogues) to help the male body not to get heart disease. 

There is no doubt that the results obtained should be very useful in clinical medicine – after all, in order for our internal clock to break, a mutation is not necessarily necessary, it is enough to bring down the daily routine yourself. The researchers themselves say that the mutation they introduced into the clock gene gives the same effect as a variety of shift work, like "a day in three", when a person is awake during the day, then at night. 

Now there is quite a lot of talk that a downed biological clock can lead to very serious health problems, and the above study once again confirms this.

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