I was recently searching for information as to in which ways coffee might be bad for one’s health, even when drunk in moderation. I was considering giving it up if there were thought to be any significant negative health effects I’d rather do without.

One of the most comprehensive-looking papers I chanced upon in my endeavors was Coffee, Caffeine and Health by van Dam et al in the New England Journal of Medicine. Below then are my summary notes of what I gleaned from it. All credit of course should go to researchers, and all mistakes in summarising are my own.

It turns out that I did not find anything that suggested much benefit in giving up my up-to-1-cup-a-day of coffee habit. In fact I was somewhat surprised to see that there are thought to be associations between drinking moderate amounts of coffee and positive health outcomes.

Another couple of links I noted that referred to some of the same data for anyone not in the mood for reading the paper itself are:

Brief summary:

  • Consumption of up to 3-5 cups of coffee daily is possible as part of a healthy diet, and in fact has been associated with a reduced risk of several diseases. However the evidence as yet doesn’t warrant recommending caffeine / coffee intake as a method to prevent disease.

  • However, high caffeine intake can have adverse effects, including exacerabating anxiety. A limit of 400mg of caffeine per day has been recommended for adults who are not pregnant or lactating, and 200mg for those who are pregnant/lactating.

  • Most, but not all, of the beneficial effects seem to be associated with decaffeinated coffee as well as caffeinated, so that is an option if sensitive to caffeine.

  • Caffeine can interfere with sleep, although this varies between people. Nontheless, drinking it late in the day may be unadvisable.

  • Unfiltered, and to some extent espresso, coffee have cholesterol-raising compounds so it may be better to limit consumption of those, but filtered or instant coffee does not have that effect.

In more detail:

Coffee and tea are amongst the most popular beverages in the world, with their substantial caffeine content making caffeine the most widely used psychoactive agent.

Caffeine content is typically highest in coffee, energy drinks and caffeine tablets, intermediate in tea and lowest in soft drinks.

In the US 85% of adults consume caffeine daily, with an average intake of 135mg a day (~1.5 standard cups of coffee).

Coffee is the main source of caffeine for adults. For adolescents, soft drinks and tea are their primary sources.

Potential issues in research on caffeine and coffee:

  • Coffee contains hundreds of other biologically active phytochemicals. Thus we should be cautious in assuming any effects of coffee are due to the caffeine alone.
  • Observing the immediate effects of caffeine may not tell us about long term effects, as tolerance can develop.
  • Epidemiological studies of caffeine intake and risk of chronic disease are potentially confounded by smoking or other lifestyle factors. Earlier studies did not account for this bias and produced misleading conclusions. Residual confounding is a risk even for recent studies thatdo adjust for potential confounders.
  • Measurement error in assessment of caffeine intake - although self-reports on frequency of coffee consumption are thought to be mostly accurate.
  • Most studies use coffee and tea intake as the dominant sources of caffeine. It’s not certain that any outcomes would also apply to other sources of caffeine.

Metabolising caffeine

The half-line of caffeine in human adults is usually between 2.5 and 4.5 hours, but can vary between people a lot.

The rate of caffeine metabolism is partially inherited.

Factors that reduce the rate of caffeine metabolism:

  • Being a newborn baby
  • Taking oral contraceptives
  • Being pregnant
  • Certain medications, including some quinolone anti- biotics, cardiovascular drugs, bronchodilators, and antidepressant agents.

Factors that increase the rate of caffeine metabolism:

  • Smoking

Caffeine can affect the actions of some drugs.

Health effects of caffeine

Positive associations

In moderate doses (40-300mg) caffeine can reduce fatigue and reaction time and increase alertness as well as vigilance during long duration tasks with limited stimulation. However it cannot compensate for lower performance after long-term sleep deprivation.

Coffee consumption is associated with a reduced risk of cardiovascular diseases, including coronary artery diseases, strokes and death from cardiovascular events. There is no increase risk of cardiovascular events in either the general population of people with a history of hypertension, diabetes or cardiovascular disease.

There is strong evidence showing that consumption of coffee and caffeine is not associated with an increased incidence of cancer or an increase rate of death from cancer.

In fact coffee consumption is associated with a reduced risk of:

  • melanoma
  • nonmelanoma skin cancer
  • prostate cancer
  • breast cancer
  • endometrial cancer (similar with caffeinated or decaffeinated coffee)
  • hepatocellular carcinoma (stronger with caffeinated coffee)

Coffee is associated with liver health, including lower levels of enzymes reflecting liver damage and a lower risk of liver fibrosis and cirrhosis. Caffeine metabolites reduce collagen deposits in liver cells. Coffee polyphenols may protect against liver steatosis and fibrogenesis.

Caffeine may improve energy balance by reducing appetite and increasing the basal metabolic rate and food-induced thermogenesis.

Increasing caffeine consumption was associated with slightly less long-term weight gain, and there’s limited evidence suggesting a small beneficial effect on body fat.

Caffeine intake reduces insulin sensitivity in the short term. But consumption of 4 - 5 cups of caffeinated coffee every day did not affect insulin resistance. Coffee reduces hepatic insulin resistances, and habitual caffeinated or decaffeinated coffee consumption is associated with a reduced risk of type 2 diabetes. This suggests the adverse effect of caffeine on insulin sensitivity is either offset by beneficial effects of other coffee components or tolerance is developed to it.

Coffee consumption is associated with a reduced risk of gallstones and gall-bladder cancer, with a strong association for caffeinated rather than decaffeinated coffee. Both types of coffee are associated with a decreased risk of kidney stones.

Caffeine intake is strongly associated with a reduction in risk of getting Parkinson’s disease, and also prevents Parkinson’s disease in animal models. This association doesn’t exist with decaffeinated coffee.

Coffee and caffeine consumption is associated with a reduced risk of depression and suicide, although this may not be true for people who consume >= 8 cups of coffee a day.

Consumption of 2-5 cups of coffee per day is associated with reduced mortality in studies across the world. The effect is similar for caffeinated and decaffeinated coffee.

Consuming > 5 cups of coffee was associated with a similar or lower risk of death than no consumption after adjustment for smoking status. Whilst confounding by baseline health status could be an issue, the effect is still seen in studies of participants who don’t have chronic diseases or poor self-rated health.

Negative associations

High levels of caffeine intake can induce anxiety, particularly on occasions >200mg are consumed, or >400mg a day, and people who are sensitive to it, including those with anxiety or bipolar diagnoses. Effects can very a lot between people.

Caffeine consumption late in the day can increase sleep latency and lower quality of sleep. Effects can very a lot between people.

Very high doses of caffeine are also associated with restlessness, nervousness, dysphoria, insomnia, excitement, psychomotor agitation, and rambling flow of thought and speech.

Caffeine can become toxics at intakes of >= 1.2g. It may be fatal at doses of 10-14g. This is equivalent to around 75-100 standard cups of coffee.

High consumption of energy drinks and shots, particularly if mixed with alcohol, has been linked to adverse cardio-vascular, psychological, and neurologic events, including fatal events. The reasons may related to consumption patterns, usage among children, lack of clarity about caffeine content and possible additive effects with other ingredients of the drinks. Recommendation here is to avoid consumption of >200mg caffeine per occasion and not to mix with alcohol.

Quitting a caffeine habit can lead to withdrawal symptoms, lasting from 2-9 days. Gradually decreasing caffeine consumption can help with these.

Unfiltered coffee has high concentrations of the cholesterol-raising compound cafestol, with expresso having intermediate levels and filters or instant coffee having almost none. High consumption of unfiltered coffee increases cholesterol levels in comparison to filtered coffee, which would predict an 11% risk increase of major cardiovascular events. In the same study, filtered coffee did not raise cholesterol levels. Recommendation is to limit consumption of unfiltered coffee, and moderate consumption of espresso.

Many caffeinated beverages, such as sugary soft drinks or creamy coffee servings, are high in calories, which could lead to weight gain.

In pregnancy, higher caffeine intake is associated with lower birth weight -associations have been seen for both coffee and tea. Also with higher risk of pregnancy loss, although less so at lower levels of intake. It may induce uteroplacental vaso-constriction and hypoxia.

Prepregnancy coffee consumption has been associated with an increased risk of spontaneous abortion.

Evidence of negative effects of caffeine on fetal health is not conclusive, but a prudent recommendation might be to limit caffeine consumption to <= 200mg during pregnancy.

No or uncertain associations

High caffeine intake can stimulate urine output. No detrimental effects on hydration have been seen with long-term consumption of moderate doses of caffeine <= 400mg per day.

Although caffeine is associated with increased blood pressure, no effect on blood pressure is found in trials of caffeinated coffee, even amongst patients with hypertension - possibly due to other components of coffee. Coffee consumption is not associated with increased risk of hypertension.

No association has been found between caffeine intake and atrial fibrillation.

Associations with dementia or Alzheimer’s disease have been inconsistent.