Are you desperate for a cup of coffee just now? The urge might be determined by your genes. I almost didn’t believe it when the newspaper reported that scientists had explored the genes of pregnant women to predict the amount of coffee they consume and its potential impact on their pregnancy.
I have been heavily involved in developing elaborate protocols to explore population food consumption in detail. And now all you have to do is look at the genes. So I did some research and it seems to be true that coffee drinking behaviour is at least partly due to genetics, with a specific set of genetic variants affecting how much coffee we drink.
What the researchers found
In the reported findings, researchers at the University of Queensland used a method called Mendelian randomisation which used eight genetic variants that predicted pregnant women’s coffee drinking behaviour and examined whether these variants were also associated with birth outcomes. Current World Health Organization guidelines say pregnant women should drink less than 300mg of caffeine, or two to three cups of coffee per day. However, the researchers through their genetic analyses found that coffee consumption during pregnancy might not itself contribute to adverse outcomes such as stillbirth, sporadic miscarriages and pre-term birth or lower gestational age or birthweight of the offspring.
As a caveat just to be on the safe side, the researchers emphasised that the study only looked at certain adverse pregnancy outcomes, and it might be possible that coffee consumption could affect other important aspects of foetal development.
This has been known for some time
The important outcome is that genetics can be used to estimate the amount of coffee consumed. This has actually been known for some time. Heritability refers to degree of genetic influence and can vary from 0 (not heritable) to 1 (completely inherited).
A review published in 2010, reported that twin studies had estimated heritability of coffee consumption by comparing monozygotic twins, who share the common familial environment and the same genes, to dizygotic twins, who also share common familial environment but only half of the genetic material. These studies found that heritability of coffee consumption varied from 0.30 to 0.60 in different populations. Heavy consumption, defined as more than 6 cups of coffee daily, had a heritability of 0.77. A few conclusions can be drawn. First, heavy consumers seem to differ from moderate and light coffee users on several accounts. Secondly, heavier coffee users appear to be more influenced by genetics than lighter caffeine users.
So far the studies confirmed the possibilities of coffee consumption inheritance without identifying the individual genes responsible for such differential inheritance pattern.
And the complicated stuff
So genetics have long been suspected of contributing to individual differences in coffee consumption. However, pinpointing the specific genetic variants has been challenging. Thus, researchers as part of the Coffee and Caffeine Genetics Consortium conducted a genome-wide meta-analysis of more than 120,000 regular coffee drinkers of European and African American ancestry. They identified two variants that mapped to genes involved in caffeine metabolism, POR and ABCG2 (two others, AHR and CYP1A2 had been identified previously). Two variants were identified near genes BDNF and SLC6A4 that potentially influence the rewarding effects of caffeine. Two others – near the GCKR and MLXIPL genes involved in glucose and lipid metabolism – had not previously been linked to the metabolism or neurological effects of coffee.
The findings suggest that genes drive people to naturally modulate their coffee intake to experience the optimal effects exerted by the caffeine in coffee and that the strongest genetic factors linked to increased coffee intake likely work by directly increasing caffeine metabolism.
But there is more
People who like to drink their coffee black also prefer dark chocolate, a new Northwestern Medicine study found. The reason is also in their genes.
The scientists found that coffee drinkers who have a genetic variant that reflects a faster metabolism of caffeine prefer bitter, black coffee. And the same genetic variant is found in people who prefer the more bitter dark chocolate over the more mellow milk chocolate.
The reason is not because they love the taste, but rather because they associate the bitter flavour with the boost in mental alertness they expect from coffee.
It is interesting because these gene variants are related to faster metabolism of caffeine and not related to taste. These individuals metabolise caffeine faster, so the stimulating effects wear off faster as well. So, they need to drink more. They learn to associate bitterness with caffeine and the boost they feel. When they think of coffee, they think of a bitter taste, so they enjoy dark coffee and, likewise, dark chocolate.
A new era
In the past, when scientists studied the health benefits of coffee and dark chocolate, they had to rely on epidemiological studies, which only confer an association with health benefits rather than a stronger causal link. The new research shows these genetic variants can be used more precisely to study the relationship between coffee and health benefits.
And who knows, in the future there might be other genetic markers found that drive our food consumption behaviour.