7 of the weirdest things coffee does to your body

Coffee is renowned for its caffeine content, which makes us feel awake and alert. However, coffee is a complex plant extract containing hundreds of bioactive compounds that can influence various aspects of our bodies in unexpected ways. Here are seven of the most unusual effects of coffee.

Firstly, coffee can prompt bowel movements. About one-third of people experience the urge to poop shortly after drinking coffee, whether regular or decaf. This is due to compounds in coffee beyond just caffeine. Additionally, your colon may be more active in the morning when most people consume their first cup of coffee. The presence of lactose in milk or certain sugar-free sweeteners can also stimulate bowel movements, especially when consumed in large amounts.

Secondly, coffee can aggravate reflux symptoms and affect eye and ear health. Reflux, where stomach acid flows back into the food pipe, can cause coughing, wheezing, and respiratory issues. Caffeine can temporarily elevate eye pressure in individuals with glaucoma or ocular hypertension, leading to potential eye damage. Moreover, there is a condition called patulous Eustachian tube dysfunction, where the tube connecting the middle ear to the back of the nose remains open abnormally, causing an unusual loudness of one's voice and breathing.

Some people with this condition may be advised to limit their consumption of caffeinated drinks and maintain hydration.

Thirdly, coffee can interact with certain medications. For instance, it can hinder the absorption of levothyroxine, a thyroid medication, and alendronate, an osteoporosis drug. Caffeine can also slow down the metabolism of the antipsychotic clozapine, raising its concentration in the bloodstream. Conversely, some medications can alter how coffee behaves in the body.

For example, the antibiotic ciprofloxacin can slow down the breakdown of caffeine, meaning your usual cup of coffee may remain in your system for a more extended period.

Fourthly, coffee can impact cholesterol levels. Coffee contains diterpenes, such as cafestol and kahweol, which can increase total and LDL ("bad") cholesterol. However, in short-term trials, these same compounds can lower lipoprotein(a), potentially indicating a reduced risk of heart attack or stroke. Other coffee compounds, like chlorogenic acids, may modestly reduce blood pressure and enhance blood vessel function. The overall effect of coffee on heart health markers remains unclear.

Fifthly, coffee may nourish gut microbes. Laboratory experiments suggest that some coffee compounds, like chlorogenic acids and complex carbohydrates called roasting products known as melanoidins, reach the colon, where gut microbes can ferment them. Small human studies indicate that drinking coffee can alter the composition of the gut microbiome. However, as the evidence is still evolving, it is premature to consider coffee as a prebiotic.

Sixthly, coffee can influence iron levels. Drinking coffee with a meal can significantly reduce the absorption of non-haem iron, which is primarily found in plant foods. This effect is not solely due to caffeine but rather the presence of polyphenols in coffee, such as chlorogenic acids, which can bind with iron in the digestive tract, hindering its absorption.

This is particularly relevant for individuals with low iron stores or those relying heavily on plant sources of iron rather than as a reason to discontinue coffee consumption with breakfast.

Lastly, coffee can initiate digestive processes in the absence of food. It can stimulate the pancreas to release trypsin, an enzyme involved in protein digestion, both in regular and decaffeinated coffee. This digestive "heads-up" may not necessarily affect feelings of hunger. Furthermore, coffee can impact gut hormones responsible for appetite and satiety, although studies have not consistently demonstrated whether this leads to increased or decreased food intake.