As the mainstream media begins to freak out about a new report in Chemical Engineering News suggesting that single portions of brewed Starbucks coffee approach or exceed “safe” daily caffeine levels for healthy adults, coffee on the whole may be in need of a little defense.
Published by the American Chemical Society, the CEN report points out that a Grande (16-ounce) Starbucks Coffee contains 330 mg of caffeine, just 70 shy of what the reported cited as a “safe” daily limit. A Venti (20-ounce), meanwhile, has contains 415 mg, exceeding the daily limit in a single pour. Incidentally, multiple newspapers have reported that Starbucks has denied the data about its caffeine levels, although no one from the company was actually quoted or cited, and the company’s own menu section backs up the CEN report’s claims.
But what may be more striking to coffee professionals is the very identification of a “safe” daily caffeine limit for healthy adults. So where did the 400 mg limit come from?: A 10-year-old Canadian government study that was essentially a survey of 200 even older studies. Here’s a description from CEN about the origin of the “safe” limit:
In 2003, a team at Health Canada, a government regulatory agency, reviewed more than 200 studies about caffeine’s effects on human health. On the basis of the survey, the team concluded that 400 mg of caffeine per day (or about three 8-oz cups of brewed coffee) is a safe dose for healthy adults to consume. At and below this level, the average person does not experience negative mood changes or heart problems, the report stated.
That said, the report continues to cite newer data that reflects a deeper scientific understanding of caffeine’s effects on the human body, largely invalidating the very concept of a “safe” daily limit.
But these recommended “safe” levels of caffeine are just statistical averages over the population. Some people tolerate caffeine and can ingest large quantities of the compound without ill effects, and others can’t, explains Emma Childs, a behavioral psychopharmacologist at the University of Chicago.
Fifty percent of the caffeine a person takes in gets cleared from the body, on average, in five hours. But studies have shown this rate can vary because of other drug use: Women taking oral contraceptives break down caffeine slower than those not on a contraceptive pill, and people who smoke process the stimulant faster than those who don’t.
Genetics also plays a big role in how a person reacts to caffeine. For example, men metabolize caffeine faster than women. Scientists have also found that certain DNA sequence variations in the gene coding for CYP1A2, the main cytochrome P450 enzyme that metabolizes caffeine, control how fast or slowly a person breaks down the stimulant. The variations, called singlenucleotide polymorphisms (SNPs), increase the levels of the enzyme present in the liver.
For more: The CEN report