What is the relationship between pregnancy and Alzheimer's?

We know more about Alzheimer's each day. We know, for example, that dementia, which is its main consequence, is caused by the progressive degeneration of neurons due to an excessive accumulation of proteins called β-amyloid and tau. This has allowed us to design new ways to diagnose the disease and also the first specific drugs that can slightly slow its progress. But we still have many unanswered questions, and one of the most important is why women have a higher risk of suffering from it.

The difference is not marginal: statistics say that up to two-thirds of Alzheimer's diagnoses are in women. If one in ten men aged 45 will eventually develop the disease, in women the probability doubles. Several reasons have been proposed, and surely all of them have a part of the truth. The most obvious is that women have a higher average life expectancy than men, up to about five years longer. In a disease that depends so directly on aging, this explains part of the differences: the more years you live, the more likely your brain is to degenerate.

But there must be other factors involved, because even if we compare people of the same age, there are more women than men with Alzheimer's. And, curiously, this gender bias is not seen in other types of dementia. The main reasons, therefore, must be related to how hormones, which are what mark the main differences between men and women, affect the course of the biological processes involved.

For example, it is known that hormonal changes during menopause could favor the accumulation of proteins that cause Alzheimer's. One of the hypotheses that could explain this is that women have a more active immune system and, therefore, during the process of fighting infections, they would generate more β-amyloid waste than normal. This hyperactivity could also lead to a higher frequency of autoimmune disorders (they are twice as common in women), which have also been seen to be related to Alzheimer's.

The number of parts influences

New evidence of this relationship between hormones and neurodegeneration has recently appeared in an article published in the journal Neurology,led by Anna Brugulat, a researcher at the Barcelonaβeta Brain Research Center and the University of Vic. In the study, scientists analyzed the reproductive history of 254 women who had already gone through menopause, and compared it with measurements of beta-amyloid protein levels and also hippocampal volume (from magnetic resonance imaging), a brain structure that is seen to shrink as the disease progresses. This group of volunteers included healthy women and also others who had positive markers for Alzheimer's and were already in the stages where symptoms begin to appear.

What they saw was that the number of births correlated with some markers: the more children they had, the more likely they were to begin to show cognitive problems and have a smaller hippocampus. The conclusion is not that giving birth causes Alzheimer's, but that the hormonal changes seen during gestation are so important that they could accelerate the processes related to the disease and make it appear earlier. For the moment, it is only a statistical association, which will need to be validated with more detailed experiments that seek whether there is really a cause-and-effect relationship.

The links between reproductive history and brain health are likely more complex. It has long been known that during pregnancy, women's brains undergo profound functional and morphological changes, primarily aimed at preparing them for motherhood. Some of these effects could be long-lasting. Earlier this year, a study was published a paper in the journal Alzheimer’s and Dementia, led by Carolyn J. Crandall, from the University of California, which analyzed 7,000 women around 70 years old and found that the more time they had spent pregnant and breastfeeding throughout their lives, the better scores they achieved on various cognitive tests. This would suggest that hormones related to these processes confer a certain protection of intellectual functions, but perhaps they are not sufficient to slow down Alzheimer's if the seeds of the disease have already been planted. In these cases, the effects would be the opposite.

Many of the factors that determine this greater vulnerability of women to Alzheimer's, such as those related to hormones, will be difficult to modify. In the future, we may have preventive drugs, but for now, to protect the brain, the most useful thing is to do what is known to reduce risks: exercise, maintain a healthy and balanced diet, avoid tobacco and other toxins, sleep well (during sleep, protein waste accumulated during the day is cleaned), and keep the brain well stimulated with social activities and those that require intellectual effort.