Almost any aspect of our lives can have some effect on our fertility although the story that wearing tight jeans reduces your sperm count doesn’t seem to be true. But broadly speaking, anything that is generally bad for you is likely to reduce your fertility somewhat.
Weight and fertility
Being overweight or underweight reduces fertility, especially in women. Pregnancy, and in some cases even menstruation, will not take place if the body does not have enough fat to support it. Think about it in terms of evolution a starving animal would need to concentrate on getting through the immediate future, rather than worrying about reproduction. Now our lifestyles can simulate starvation – in anorexics the situation may be so extreme that they stop menstruating, let alone being able to conceive.
Weight, for the purposes of fertility as well as for much else, is analyzed by means of the Body Mass Index (BMI). This is a simple calculation: your weight in kilograms, divided by the square of your height in meters. This will give you a number, which you can compare to averages over a population. A figure of between 20 and 25 is usually seen as medically ideal. Remember, though, that this isn’t a universal truth, and you should consult a medical professional for advice on your particular circumstances.
Obesity wreaks its damage to fertility by means of hormones. Chemically, cholesterol (which is often found at high levels in the obese) is very similar to estrogen (the hormone controlling much of the menstrual and female reproductive cycles). If there is too much cholesterol in the body, the adrenal gland will convert some of it into ‘ androstenedione’, which in turn gets converted into estrogen. The body will therefore contain too much estrogen, which will disrupt reproduction.
Even if you are a perfect weight now, if you have been obese or underweight in the past, this could still have an impact on your fertility. There is particular evidence that teenage obesity has an ongoing impact on fertility. There is believed to be a link between female obesity and Polycystic Ovary Syndrome (PCOS), although it remains unclear how this interacts with the genetic basis of the condition. If you do succeed in conceiving, being overweight can lead to complications during pregnancy, increasing the risk of miscarriage and birth defects.
Excessive exercise can reduce fertility for both sexes. The key word here is ‘excessive’: taking regular moderate exercise is unlikely to harm your fertility. In fact, moderate exercise will, if anything, improve fertility by way of improving your general health. We still don’t understand why exercise affects fertility. One theory is that exercise uses up energy. The body might plausibly interpret an energy deficiency as an indication that it does not have enough spare energy to engage in the energy-intensive business of reproduction.
This theory, though, has suffered a blow from evidence that exercise harms fertility even in people who are getting a good diet. We are left without much idea of what it is about exercise that reduces fertility.
Looking at people’s fertility in connection with their occupation is a bit of a cheat. Rather than directly trying to find specific chemical, medical or social causes of infertility, we compile statistics on the fertility of people in different walks of life, and try to spot the careers which are bad for your fertility.
What the statistics tell us is that miners, farmers, construction workers and car mechanics have an elevated risk of fertility problems. Women, in addition to these risks, can also have their fertility reduced by looking at computer screens.
These findings need to be taken with a large pinch of salt. Remember the adage that “correlation does not equal causation”. Just because two things are seen together, we can’t assume that one causes the other. It is almost impossible to separate out the effects of different factors which are associated with occupation. Are farmers less fertile because they are unusually likely to suffer depression? Does the physical exercise involved in being a miner account for their lower fertility? Some of these links are easy to spot, but eliminating them all is painstaking work.
Alcohol abuse (and, to a lesser extent, even moderate drinking) harms the fertility of both sexes. Alcohol damages the liver, and this in turn disrupts the balance of hormones in the body, for example by increasing the amount of estrogen produced by men. Such hormonal imbalance affects the entire body, but particularly harms the production of sperm. Alcohol can also have a direct toxic effect on the cells in the testes which produce sperm.
For women, drinking alcohol can disrupt both ovulation and the menstrual cycle. But the biggest damage is done through drinking after conception those who drink when pregnant risk miscarriage or stillbirth, as well as a range of birth defects. So, in short, both men and women need to cut back on the alcohol if they’re having trouble conceiving, and if they do succeed then abstinence over the course of pregnancy is a must.
Smoking causes infertility, according to the warnings many countries require on cigarette packets. They’re telling the truth, and although scientists haven’t yet untangled all the connections between smoking and fertility, we already know enough to know that it’s bad news.
Survey after survey has shown that smokers have more fertility problems than non-smokers. Smokers have lower sperm counts and higher levels of abnormal sperm, and stopping smoking leads to an increase in sperm count. But it’s one thing to know smoking harms fertility, and another to untangle which of the dozens of toxic chemicals in cigarette smoke is responsible, and why.
Some of these find their way into the semen where, of course, they wreak their toxic damage on the sperm. Meanwhile, the negative effects of smoking on other parts of the body will be increasing blood pressure and bringing hormones out of balance both factors linked to reduced fertility.
Smoking damages DNA in the body, including in sperm cells. If sperm with smoke-damaged DNA fertilizes an egg, there is an increased risk of childhood cancer and other health problems in the child.
The good news is that fertility increases once you stop smoking, although it may, for example, take a few months for sperm counts to return to a normal level.
Despite ever-increasing evidence of the negative health impact of caffeine consumption, our culture does not treat it as a drug. But a drug it certainly is, and its effects on the body can be dramatic. This may include effects on fertility: some studies have found statistical evidence for a link, but we have no understanding of why there would be one.
The evidence seems to suggest that drinking a daily cup of coffee can increase the time taken to get pregnant, while another survey claims that drinking 2-3 cups each day when pregnant increases the risk of a miscarriage.
Other recreational drugs may have equal or greater impacts on fertility. These have been less intensively studied than alcohol and tobacco, not least because of the practical difficulties of conducting human tests with banned substances.
Smoking marijuana, according to a team of researchers from Buffalo University, reduces the quantity of semen, the number of sperm in the semen, and the percentage of those sperm that are functional. Marijuana seems to have an adverse effect on the ovaries when smoked by women. Unlike with smoking tobacco, there is no evidence to indicate whether fertility will increase again if you stop smoking marijuana.
During pregnancy, illegal drug use can easily affect the baby, leading to miscarriage, stillbirth, and birth defects.