The Coffee Consumption Genes

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.

A Word About Zinc

I assume you’re not too worried about zinc intake. This might be correct for most people in the developed world, with some important exceptions, as zinc is naturally found in a wide variety of both animal and plant foods. Still you should be aware that we all need a constant supply of zinc as it is considered an essential nutrient for the human body involved in numerous different processes.

However, worldwide zinc deficiency can be a serious problem as it affects about two billion people in the developing world and is associated with many diseases. Zinc deficiency causes growth retardation in children, delayed sexual maturation, infection susceptibility, and diarrhea.

Consumption of excess zinc may in turn cause ataxia, lethargy, and copper deficiency. So a balance is important.

The magic of zinc

Zinc is the second most abundant trace mineral in our bodies after iron and is present in every cell. It is necessary for the activity of over 300 enzymes that aid in metabolism, digestion, nerve function and many other processes. It is critical for the development and function of immune cells and is also fundamental to skin health, DNA synthesis and protein production. Zinc deficiency can lead to a weakened immune response, particularly important in covid times. Zinc supplements can significantly reduce the risk of infections and promote immune response in older adults

Body growth and development relies on zinc because of its role in cell growth and division. Zinc is commonly used in hospitals as a treatment for burns, certain ulcers and other skin injuries. Because it plays critical roles in collagen synthesis, immune function and inflammatory response, it is necessary for proper healing.

Oddly, zinc deficiency will reduce our ability to taste or smell our food and surroundings because one of the enzymes crucial for proper taste and smell is dependent on this nutrient.

A pretty impressive list.

Too little or too much zinc intake

Although severe zinc deficiency is rare, milder forms of zinc deficiency are more common, especially in children in developing countries where diets are often lacking in important nutrients. Symptoms of mild zinc deficiency include diarrhea, decreased immunity, thinning hair, decreased appetite, mood disturbances, dry skin, fertility issues and impaired wound healing.

Just as a deficiency in zinc can cause health complications, excessive intake can also lead to negative side effects. This is mainly related to going overboard with consumption of too much zinc through food supplements. Symptoms of toxicity include nausea, vomiting and loss of appetite. It can cause diarrhea, abdominal cramps and headaches. Ingesting too much zinc can also interfere with the absorption of copper and iron.

Zinc’s immune-boosting properties

The importance of zinc for a properly functioning immune system is intriguing. Although well known in principle, new details have recently come to light.

Results published in 2022 by scientists at the Fred Hutchinson Cancer Center in Seattle looked at the importance of adequate zinc intake to boost immune function. They revealed two ways that the mineral supports immunity and suggested how it could be used to improve health. The team discovered that zinc is needed for the development of disease-fighting immune cells called T cells and prompts regeneration of the thymus, the immune organ that produces T cells.

The scientists found that the thymus of mice deprived of dietary zinc shrink and produce notably fewer mature T cells, even after as little as three weeks of a no-zinc diet. They also showed that without zinc, T cells cannot fully mature. Conversely, with extra zinc T cells recover faster than normal.

They are now looking into how zinc may fit in with how the immune system repairs itself after stressors like chemotherapy, blood stem cell transplant and radiation exposure or how zinc can assist people with chronic immune decline that accompanies ageing.

Vulnerable population groups

Although zinc deficiency is uncommon, vegetarians, some pregnant women, 7-12 months old infants, alcoholics and people with some digestive disorders need to consider their zinc intake.

The bioavailability of zinc from vegetarian diets is lower than from non-vegetarian diets. In addition, vegetarians typically eat high levels of legumes and whole grains, which contain phytates that bind zinc and inhibit its absorption.

Pregnant women, particularly those starting their pregnancy with marginal zinc status, are at increased risk of becoming zinc insufficient due, in part, to high fetal requirements for zinc. Lactation can also deplete maternal zinc stores.

Breast milk provides sufficient zinc for the first 6 months of life but does not provide recommended amounts of zinc for infants aged 7–12 months. In addition to breast milk, infants aged 7–12 months should consume age-appropriate foods containing zinc.

Up to 50% of alcoholics have low zinc status because ethanol consumption decreases intestinal absorption of zinc and increases urinary zinc excretion. In addition, the variety and amount of food consumed by many alcoholics is limited, leading to inadequate zinc intake.

Digestive disorders such as ulcerative colitis, Crohn’s disease, and short bowel syndrome can decrease zinc absorption and increase endogenous zinc losses. Other diseases associated with zinc deficiency include malabsorption syndrome, chronic liver disease, chronic renal disease, sickle cell disease, diabetes, malignancy, and other chronic illnesses. Chronic diarrhea also leads to excessive loss of zinc.

So where to find zinc?

Many animal and plant foods are naturally rich in zinc, making it easy for most people to consume adequate amounts.

Foods highest in zinc include fish and shellfish, meat and poultry, legumes, nuts and seeds, dairy products, eggs, whole grains and vegetables like mushrooms, kale, asparagus and beet greens.

There is a caveat.

As is often common for minerals, animal products contain zinc in a form that is easily absorbed by the body. On the other hand zinc in plant-based sources is absorbed less efficiently as phytates—which are present in whole-grain breads, cereals, legumes, and other foods—bind zinc and inhibit its absorption. Thus, the bioavailability of zinc from grains and plant foods is lower than that from animal foods, although many grain- and plant-based foods are still good sources of zinc.

Clearly most people meet the recommended daily zinc intake of 11 mg for men and 8 mg for women through diet. Although I am normally not a fan of food supplements, there might be a case for using supplements containing zinc as the main ingredient for older adults and people with diseases that inhibit zinc absorption. I might even consider using a zinc supplement myself.

However, remember that high-dose zinc supplements can lead to dangerous side effects, so it’s important to stick to recommendations and only take supplements when necessary.