Nutrition Nuts and Bolts

By Shelly Najjar

The title of this post was my research question for a class paper last quarter, and I wanted to share what I learned with you.

Some background

Alcohol is metabolized (broken down) in the liver, usually by an enzyme called alcohol dehydrogenase (ADH). In the late 70’s, a couple of researchers  did a study on whether women in different phases of their menstrual cycle were affected differently by the amount of alcohol they drank (citation: Jones and Jones, 1976, Ann NY Acad Sci). It was a poorly designed study, so most scientists discussing this study don’t consider it strong of a conclusion as it could have been, but you’ll still hear people state that there may be effects.

Why it’s plausible

Throughout the menstrual cycle, levels of estrogen and progesterone (hormones) rise and fall. Researchers (citation: Holdstock and de Wit, 2000, Psychopharmacology) thought estrogen was going to increase euphoria and a drinker’s preference for alcohol, because they both can act on the dopamine system in the brain. They guessed that progesterone would increase sedation (sleepiness) and decrease ability to do tasks (impaired performance), so the effects of alcohol (which also does these things) may seem stronger. On the other hand, estrogen was thought to increase ADH activity (it would work better and faster), which would lead to faster elimination (citation: Mumenthaler, 1999, Alcsm Clin Exp Res).

So, overall, it was thought that at certain times of the menstrual cycle, the effects of alcohol may be more intense, but that it wouldn’t last as long.

What the research says

Although there are several older studies on the topic, their study designs (how they set up the study) were not very good. There are now three things that researchers say are essential for any study on this topic:

•  Use a within-subjects design (testing different things on the same person at different times in their menstrual cycle, rather than testing different things on different people at different times). This allows better comparison, since it limits the effects of variation between individual people.

• Confirm menstrual cycle phase using hormone testing (rather than just relying on counting days since the last period). This increases accuracy, since there is variation and inaccuracies if you just count days.

• Don’t use people with anovulatory cycles (a cycle when the egg does not get released). This is important because estrogen and progesterone don’t rise when this happens, so effects caused by changes in estrogen and progesterone won’t be seen (citation: previously mentioned Mumenthaler article).

I looked at two studies because they had these three features and were fairly recent.

Study #1: Holdstock and de Wit, 2000 (cited earlier)

These researchers used 16 women who each usually drank an average of 3.5 alcoholic drinks and 6 caffeinated beverages each week. Participants didn’t use drugs for at least 12 hours before and didn’t eat at least 2 hours before the test. Women were tested at 4 times through their cycle, each time being tested in the evening with spiked, sugar-free Kool-Aid. Each person drank 3 drinks over an hour, and their BAL (breath alcohol level) was tested. In addition, each woman did tasks that measured eye movement and mood.

After statistical analysis, this study didn’t show any effect of menstrual cycle on alcohol effects.

The study report was detailed and all measures, tests, and kits they used were reported (this makes a study more repeatable because another researcher has enough details to use the same technique to verify the results). Tests were done in a laboratory setting, which the researchers listed as a strength because it decreased the effect of the environment (example, you don’t have other people in the bar talking or flirting, or music playing, etc). However, this means that generalizability to a “real-world” setting is limited (do you act the same in a bar and a lab?). Although the researchers tested many phases, they decided not to test when estrogen was highest (during ovulation, when the egg is released), because it is very difficult to schedule people to come in for testing (ovulation period is only 2 days long). The researchers admit that there may be the possibility that the effect of estrogen on alcohol is only seen at high levels of estrogen, but since they didn’t test it, we don’t know. Finally, there were only 16 people in this study, but the measurements they used were accurate enough to detect a single drink’s effects, so if there was an effect that wasn’t noticed, it could be because the effect of menstrual phase is smaller than the effect of one additional drink.

Study #2: Corrêa and Oga, 2004 (citation in J Stud Alcohol)

This study used 10 women who, on average, drank 3 alcoholic drinks each, per week. Each woman didn’t use alcohol or drugs 30 hours before the tests, and had no food at least 6 hours before sessions. Women were tested at 2 points in the menstrual cycle, each test started in the morning, and lasted for 6-7 hours. Each person drank Scotch whiskey over a 10 minute time period, and then were tested throughout the day for BAL. Women received a “standard midday meal” 2 hours after they drank the whiskey, and “afternoon snacks” later in the day.

After statistical analysis, researchers didn’t find that menstrual cycle affected alcohol metabolism or elimination.

Like the first study, the tests and kits that were used to determine hormone levels were reported, which increases the study’s repeatability. In addition, since they only tested two phases of the menstrual cycle, it was good that they chose two with the largest potential difference in hormone levels. This would have the best chance of showing whether changes in menstrual cycle hormone levels affect alcohol metabolism. However, food and fasting can both affect alcohol metabolism, but the researchers never discussed this issue, although it has been noted that food, menstrual cycle, and alcohol can all change the amount of time it takes for things that go in your mouth to come out the other end. Although one study (the Mumenthaler study mentioned earlier) found that a “nonfatty breakfast” 1 hour before drinking doesn’t change BAL, the current study didn’t mention that, or the specifics of what they fed the participants.

Why it matters

Although these two studies used different approaches, they both came to the same conclusion, which also agrees with what is considered to be one of the best studies on the topic (Mumenthaler study mentioned earlier).

The implications of these results could range from research settings to social settings. In research, if the menstrual cycle doesn’t affect the metabolism of alcohol or the effects caused by drinking, then researchers may not have to control for which phase of the cycle female participants are in. As noted before, the lab setting is very different from social settings. Also, the doses used in many studies are higher than that of a standard drink and are usually consumed without food (and without having eaten for many hours). With a higher alcohol intake but less food to slow down absorption, you would think that any effects (if they exist) would be more obvious. Still, there is reason to be cautious because although alcohol levels may not be affected by the menstrual cycle, the effects may be seen with some of the things alcohol gets broken down to in the body.

So, like every research topic, more research is needed. However, if you do decide to drink, please do so with moderation, and know your body. If you think alcohol affects you differently at different times, be smart and adjust your intake. 

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Shelly Najjar, MPH, RDN is a Registered Dietitian Nutritionist and wellness coach at Confident Nutrition. You can find her on Facebook, Twitter (@ShellyNajjar), and LinkedIn.

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