Myers explained that the oft-cited 400-milligram limit has been out of date for a while. It came from the last research review, which was done in 2003 by Health Canada. Her colleagues were surprised to learn it had been that long, and that even at the time the review wasn’t really comprehensive. So they did a systematic review, meaning they followed a comprehensive, transparent protocol defined by the Institute of Medicine.
The team reviewed scoured more than 700 studies on the safety of caffeine at various levels and noted whether adverse health effects occurred above, below, or at 400 milligrams. Those health effects ranged spanned cardiovascular, musculoskeletal, reproductive, and behavioral domains. And it seems that for healthy adults, 400 milligrams is indeed a safe daily limit. For pregnant women, it’s safer to use 300 milligrams or less.
Above those levels the team found evidence of links to everything from depression and dysphoria (general unhappiness) to anxiety to hypertension to higher proportions of sperm with DNA damage.
So does that mean that 500 milligrams a day is definitely unsafe?
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