The quality of sperm decreases, but are we heading towards a sterile world?

The quality of sperm decreases, but are we heading towards a sterile world?


Thanks to the premiere of the series The story of the maid, based on the homonymous novel by Margaret Atwood, and a recent study that affirms that the quality of male sperm is decreasing worldwide, fertility is in the spotlight. Many people want to find out if the dystopian future created by Atwood, in which the world has become sterile, is really possible. Are we already halfway there?

The results of the study

The scientific article what last summer he grabbed the headlines of all the planet It revealed that the amount of sperm in Western men is decreasing.

The study is a meta-analysis that brings together studies of the same type and combines their results. Each analysis is made with data from different men evaluated at different times by different researchers. Therefore, the study is not as enlightening as it could be if the same subjects had been studied over time. In addition, many of the individual studies analyzed have shown their own problems.

So, is fertility really decreasing?

The current estimate notes that Western males produce 50 million sperm per milliliter ejaculated, that is, less than before. In any case, only one sperm is needed to fertilize an egg, so the figure of 50 million is enough to indicate that men still do not have a serious problem.

There is data that indicate that, with a number less than 40 million, there is a direct relationship between the number of sperm and the probability that the woman will become pregnant. The World Health Organization (WHO) He points out that the minimum for a man to be considered fertile is 15 million sperm per milliliter. This data is based on men who have conceived a child in the last 12 months. Only 5% with quantities below 15 million was able to reproduce.

In the case of women, it is necessary to understand that the period of time in which they are fertile is in itself short, and that it is decreasing as the educational level of women grows and the dedication to their professional careers.

The moment in which women have a greater number of ovules is during their own pregnancy in the womb of their mother. About one sixth of the ovules disappear at birth, and at puberty the number is 500,000 or even less. From puberty to 37 years there is a constant decrease, from 500,000 to 25,000 ovules. After 37, the rate of decrease increases until the arrival of menopause, when only about 1,000 ovules. It is important to note that these are only averages and that it can be ensured that a woman keeps 25,000 eggs at age 37.

Quality is another matter. Chromosomal problems (such as Down syndrome, in which a person has three copies of chromosome 21 instead of two) are increased with age. In vitro fertilization is often considered as a way to overcome fertility, but the highest percentage of success (41.5%) occurs in women under 35, and it measures pregnancies, not births. At age 40, the percentage decreases to 22%, and at 43 years it drops to 5%.

In summary, the situation for women is not perfect, but the figures do not change over time. In fact, the estimates they have not changed from 1600 to 1950.

The story of the maid

Frame from the series 'The Tale of the Maid'

What is affecting fertility?

A key factor that determines female fertility is the education. But not individual education, but that of society as a whole. If a community is cultured, fertility drops. The higher a woman's educational level, the lower the likelihood of getting pregnant during her youth.

But being able to delay the moment of motherhood is not everything. The chosen lifestyle is very important. We know that tobacco, alcohol and obesity affect the quantity and quality of ovules. The women, as we have commented previously, have the highest number of ovules when they are in their mother's womb and, if this one smokes, it will directly affect the ovules of the fetus. Tobacco use during pregnancy is slowly decreasing (from 15% in 2009 to 11% in 2014), but the percentage among indigenous populations, such as those in Australia, is still very high (45%).

It has always been said that tobacco and alcohol are the main factors for the decrease in the number of sperm, but the evidence doubts this data. Studies suggest that obesity and stress are the main reasons for this decline. For example, high levels of anxiety and stress have been related to low records of sperm Also the vital stress (defined as two or more stressful events happened in the last 12 months) produces that effect, but not the stress derived from work.

For men, simple figures are a clear measure of fertility. It is the quality of the sperm produced that worries. The WHO states that for a man to be considered fertile at least 4% of his sperm must have good appearance. But, in reality, it is really difficult to know which of the many factors involved may be affecting the appearance of the sperm.

Studying a small subset of society is not a good example of what happens in that society.

Studying a small subset of society is not a good example of what happens in that society.

The problems when it comes to studying fertility

We can debate about what studies say about fertility, but in Australia there are several problems inherent in research in this field. Many of the data we have on the amount of sperm come from two sources: men who go to fertility clinics and men who undergo medical tests before joining the army. The first source sticks to those who, surely, have a prior problem. The second, on the other hand, is limited to a single age group.

Meta-analyzes combine the results of many studies and are limited to collecting those that use the same tools and maintain the same approach to be compared fairly. An extensive meta-analysis indicated that smoking is harmful, but the subjects under study were male patients of a fertility clinic, so surely most of them were sterile, whether they smoked or not.

Another large study was conducted with soldiers from the US and Europe and found no relationship between fertility and alcohol consumption. This could be due to the fact that he only took into account the alcohol ingested the week before the medical tests, and it is probable that many soldiers did not drink alcohol the days before the test.

Could we extinguish?

The birth rate is lower than it should be for the replacement of the total population in USA, Australia Spain and many other countries, but the global population as a whole continues to grow and age.

At the beginning of this century women between 30 and 34 years old had more children than those in the group between 25 and 29 years old, and women between 35 and 39 exceeded in maternity those of the group between 20 and 24 years.

Currently, in Australia adolescent pregnancies (between 15 and 19 years) they are equal to late pregnancies (from 40 to 44).

The quality of sperm and eggs is more important than the figures. While we continue to investigate what quality will mean for future generations, we can be sure that Infertility is related to the increase in mortality rates. The males diagnosed sterile have increased risk of diabetes, ischemic heart disease and addiction to alcohol and drugs.

Ultimately, it's not about numbers, it's about quality. We are not only talking about the chances of having a child, but about having a healthy child. In addition, it is important to know that fertility is a thermometer that measures overall health. Although nothing indicates that we will soon be extinct (or, at least, not for reproductive reasons), the quality of sperm could be a sign of broader health problems, and should be investigated further.

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