Coffee, Tea, and Caffeine

Coffee is a new-fangled drink compared to traditional ones like tea, beer, or wine. The first records of coffee consumption are from Sufi shrines in Yemen in the Middle East in the 15th century ^¹. From that late start, coffee has become a worldwide favorite everywhere, ranking as one of the world’s top three beverages (water, tea, coffee).

Coffee Benefits

While the benefits of coffee may come from both the caffeine and the other polyphenols in it, most studies look at the effects of caffeine and coffee together. Here are some of the benefits:

Increases Energy

This benefit is clearly from caffeine. Caffeine hits the bloodstream quickly, absorption starting 15 minutes after drinking and the energy boost peaking about 30-60 minutes later. As a result, alertness increases ^² along with endurance, improving performance by 12%, according to one meta-review of studies ^³. The World Anti-Doping Agency had caffeine on its list of banned substances until 2004 when it decided it was too hard to distinguish between caffeine doping and someone who just had coffee for breakfast ^⁴.

Reduces Cardiovascular Disease

With just 1-2 cups of coffee per day, cardiovascular risk is reduced by 24%, according to a study of nearly 500,000 people in the UK Biobank database ^⁵. looked up analyses on how coffee does this and read stuff like “caffeine blocks SREBP2 activation” and “[caffeine lowers] blood proprotein convertase subtilisin/kexin type 9 (PCSK9) levels,” ^⁶ which means… I don’t understand why coffee reduces cardiovascular disease, but it does!

Reduced Digestive Diseases

Coffee helps liver function, preventing liver cirrhosis ^⁷ and helping the digestive system by improving the microbiome composition in the gut ^⁸. The same Biobank study showed a reduction of 58% in death from digestive diseases ^⁹ from one or more cups of coffee per day.

Prevents Depression

In addition to the energy pick-up mentioned above, coffee reduces the risk of depression. A meta-analysis of coffee consumption found a 24% less chance of depression in those with higher intakes of coffee ^¹⁰. The relation was a j-curve — up to about two cups per day was better, with less benefit after that.

The Best Coffee for Health

I’m not going to debate the merits of Kilamanjaro vs. Hawaiian coffee, but brewed or filtered coffee is healthier than instant or decaffeinated. In a further analysis of the UK Biobank data, Chieng et al. found a reduction in death from all causes by 27% for brewed coffees (including espressos and lattes). In comparison, brewed, decaffeinated coffee only provided a 14% reduction, and instant coffee provided an 11% reduction, which implies that about half of the benefit of coffee is from caffeine ^¹¹. The other half is from polyphenols or other things that are apparently lost in the process of making instant coffee.

Confounded Smoke

People who smoke often drink coffee as well, which can mask the observed benefits of coffee. Early research appeared to show that coffee had no benefit because of the correlation with smoking ^¹². Unfortunately, most studies on coffee use a “smoking yes/no” flag instead of asking how much people smoke, which misses interactions between the amount of smoking and coffee. For example, people who drink a lot of coffee might smoke more, and one effect of nicotine is that it makes smokers digest coffee faster, which might make them drink more coffee^¹³. A 2016 study that separated smokers and non-smokers found that coffee’s benefit was primarily linear, with additional benefits of up to eight cups daily. However, the first two cups provided the most benefit.

Cautions

Sleep Interference

Coffee isn’t a substitute for sleep, and the caffeine in coffee can disturb sleep, even though it might not be noticed. Taking 400 mg of caffeine even six hours before sleeping doubled the time it took to fall asleep and reduced total sleep time by about 9% ^¹⁴. The subjects who took this caffeine six hours before were unaware of their reduced sleep.

Pregnancy

Some studies with coffee or caffeine show results that should give pause for those pregnant or looking to become so. Pregnancy advice is far from my normal study area, and kids are precious, so consider your coffee and caffeine intake when considering pregnancy.

Tea

Although tea has long roots in history and culture, on the longevity figures, when comparing it with coffee, tea seems like coffee-lite. It has about half as much caffeine as a cup of coffee and about half as many polyphenols, which are good chemicals in plants, like flavonoids. Likewise, in studies that list the benefits of coffee and tea, tea’s benefits are similar to coffee, but with double the dosage — “1-2 cups of coffee or 2-4 cups of tea ^¹⁵.” That increased volume requirement could cause additional interference from smoking, as mentioned above.

Large studies from Japan have found a comparable benefit from green tea benefits as black tea^¹⁶, which isn’t surprising since they’re from the same plant with a comparable amount of caffeine^¹⁷.

FAQ

Does coffee dehydrate you?

While the caffeine in coffee can cause a diuretic effect in large doses, the effect is minor. In a controlled study, coffee drinkers drank four cups of water or coffee for several days. Testing shows no significant change in hydration after drinking coffee compared to the water ^¹⁸.

Does coffee make you poop?

Yes, at least for some people. This effect is partly because of the caffeine, which stimulates the colon and intestinal muscles ^¹⁹, but decaffeinated coffee also has some effects, so it’s not just the caffeine. Other effects of coffee are the chlorogenic acids, which increase stomach acidity, speeding up digestion ^²⁰. Hot water doesn’t have the same effects, so cold coffee should be as effective as hot coffee. In any case, the impact seems to be about 10-15 minutes after drinking, up to 45 minutes later, so plan accordingly.

Does coffee stunt your growth?

No. It’s unclear where this misconception came from, but medical experts agree that growth is normal in coffee drinkers ^²¹.

Does coffee make you fat?

Coffee alone won’t make you fat. The caffeine in coffee boosts metabolism ^²², which burns an extra 79 calories daily. That said, coffee with added sugar can quickly overwhelm that slight benefit. For example, a Starbucks Caramel Frappuccino Grande has 370 calories, or more than half a regular meal ^²³. Also, coffee drinking later in the day could disrupt sleep patterns, as mentioned above, which has adverse effects on weight ^²⁴.

Does coffee increase blood pressure?

While people who don’t often drink coffee may experience a short-term increase in blood pressure of a few points, regular coffee drinkers don’t show any increase in blood pressure ^²⁵.

Does caffeine help with headaches?

Caffeine can help with headaches but also cause them. This is because caffeine causes veins to constrict. If you have a headache, this constriction of the veins can relieve some of the pressure, reducing the pain. Some painkillers, like Anacin, contain caffeine for this reason.

On the flip side, if you regularly consume caffeine, the body can become used to constricted veins, and if the caffeine intake is stopped, the veins swell, causing a headache. This caffeine withdrawal headache can last a couple of weeks ^²⁶.