Alcohol, Smoking, Caffeine and Fertility
Understanding studies about lifestyle and fertility
Many investigators have attempted to determine whether lifestyle factors such as the amount of alcohol, tobacco or caffeine that is consumed by a person can affect their fertility.
The studies are usually performed as population surveys. In a population survey, the researcher will give a questionnaire to a large group, for example, all women attending an infertility clinic over a period of time. They will compare those answers to those of a “control” group, such as women attending a clinic for prenatal care (already pregnant) and who deny any problems conceiving.
The researcher will then compare the answers given. Lets say, for example, that 50% of the women in the infertility clinic report drinking alcohol more than once per week and in the group of women with normal fertility, only 30% report drinking that much.
This may lead to the conclusion that alcohol use is ASSOCIATED WITH infertility. It does not prove that alcohol causes infertility! Why not? From the way the question was worded, we don’t know if the infertile women used alcohol first and that led to their infertility or if they had infertility and the stress caused them to drink more. The investigator hasn’t proven a cause and effect relationship, in other words, that the alcohol actually causes the infertility. In addition, in the survey, there could be several sources of error :
- Perhaps the fertile women under reported their alcohol use
- Either group could have been inaccurate in their recollection of how much alcohol they used since they didn’t keep a diary and were just asked to recall their use over a long period of time.
- There could have been a “subgroup” of women in the infertile group who had a large amount of alcohol use, and this group threw off the results for all the infertile women.
- There could have been another “unmeasured” variable that was causing the problem. For example, let’s say that most of the women who report drinking alcohol also smoke cigarettes and it’s really the cigarette use that was causing the infertility
There are other ways to look at this question. Instead of surveying groups of infertile and fertile women to look at alcohol use, the investigators could have looked at women who report drinking alcohol versus those that don’t and instead ask them about their difficulty in achieving pregnancy. The data might then look like this:
50% of women that we found who say they drink any amount of alcohol report they had difficulty achieving pregnancy at some point in their life.
Only 10% of women who said they never drink alcohol reported difficulty in achieving pregnancy.
So what’s the best way to determine if alcohol really causes infertility? The best way is to design an experiment where women are chosen at random and divided in to groups. Group 1 would receive alcohol. Group 2 would receive a placebo that smells and tastes like alcohol but has no effect in the body. Both groups would then be monitored over a period of time to determine if they developed difficulty achieving pregnancy. Unfortunately, this type of experiment would be extremely difficult (if not impossible) to do.
We must, therefore, do the best we can with those studies which are easier to do but perhaps not give us information which is quite as conclusive.