One day we hear drinking coffee daily is good for you, the next day we hear it's bad for you. Caffeine is at the center of the never-ending debate of whether it helps you live longer or kills you faster. Now, researchers with the International Life Sciences Institute suggest drinking up to four cups of coffee a day is not linked to any harmful health effects.

"This Systematic Review provides evidence that furthers our understanding of caffeine on human health," said Dr. Eric Hentges, Executive Director, ILSI North America, in a statement.

Read More: The Median Lethal Dose Of 3 Popular Drinks That Can Kill You

In the study, published in the journal of Food and Chemical Toxicology, Hentges and his colleagues found the previously-defined levels of caffeine intake in healthy caffeine drinkers is not associated with detrimental side effects on health.

Previous research has cited assessments of caffeine safety issued by Health Canada that warn against the health risks of drinking copious amounts of caffeine. Since 2003, over 10,000 papers have been published related to caffeine, with hundreds focusing on its human health effects. According to Hentges and his colleagues, none have done a comparative analysis on these topics.

So the researchers decided to conduct what's known as a systematic review of data published from 2001 to 2015 to confirm or put to bed, the controversies surrounding caffeine's effect on health. More than 740 studies were analyzed to review caffeine-related side effects in five areas, including acute toxicity, bone/calcium, cardiovascular, behavior, and reproductive and development in four healthy populations, including adults, pregnant women, adolescents, and children. They compared the effects of 400 milligrams/day (4 cups of coffee) for adults; 300 mg/day (3 cups of coffee) for pregnant women; and 2.5 mg/day for children and adolescents.

The findings revealed the average daily consumption of caffeine across all age groups is 165 mg, with 105 mg coming from coffee. Furthermore, the researchers confirmed about 400 mg of caffeine was safe for healthy adults, but pregnant women are recommended to drink less than 300 mg a day. Children can consume up to 2.5 mg a day without experiencing any health side effects.

This coincides with the 400 mg/day of caffeine limit set by the Mayo Clinic for healthy adults. Drinking more than four cups a day is linked to migraine headache, insomnia, stomach upset, and a fast heartbeat among many others. However, some people are more sensitive to caffeine than others, so caffeine levels should be adjusted on a case-by-case basis. Factors that influence caffeine sensitivity include genetics, body mass, age, medication use and health conditions, such as anxiety disorders.

Hentges and his colleagues concluded there should be a shift in caffeine research to focus on its side effects on unhealthy populations (i.e., individuals with preexisting conditions), sensitive populations (individuals with risk-taking behavior), and interindividual variability (epigenetic trends).

"This review, being one of the first to apply systematic review methodologies to toxicological assessments, also highlights the need for refined guidance and frameworks unique to the conduct of systematic review in this field," wrote the researchers in their abstract.

Read More: Why Skipping Your Morning Cup Induces A Caffeine Withdrawal Headache

However, they do caution one population to drink at their own risk: pregnant women. Currently, the National Institutes of Health states women who drink more than two caffeinated beverages a day are more likely to miscarry during the weeks leading up to conception. They did find women who took a daily multivitamin before conception and through early pregnancy were less likely to miscarry than those who did not.

It's important to note the new study was funded by ILSI, while the American Beverage Association, and the National Coffee Association also donated towards the research.

Remember, everyone has their own safe limit for coffee, but it should not exceed more than four cups a day.

Source: Wikoff D, Welsh BT, Henderson R et al. Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food and Chemical Toxicology. 2017.

See Also:

Science-Backed Benefits Of Coffee Reveal Its Impacts On Everything From Heart To Brain Health

Health Benefits Of Caffeine