You may want to rethink your next sushi order: The mercury concentrations in Hawaiian yellowfin tuna (also known as ahi tuna, a popular fish for rolls and sashimi) are increasing by 3.8 percent or more per year, report researchers from the University of Michigan . Scientists have suspected this might happen for decades. The mercury concentration in ocean water is also steadily climbing, but this is the first study to confirm suspicions.

Why this matters: Mercury can accumulate in your body over time. Eat foods that contain the heavy metal too often, and you risk toxicity or poisoning, a potentially life-threatening condition that causes muscle twitches and weakness, headaches, mood swings, and brain fog or memory lapses. (High-mercury fish are a Mistake for Your Hair and Nails too.) It's especially dangerous for pregnant or trying women, kids, and those with heart disease.

So what's a sushi-loving girl to do? The study authors don't say, and how much fish is safe to eat varies per person, based on current mercury levels, age, and overall health, says Ashley Koff, R.D. (She says to stick to lower-mercury options, and to use the Environmental Working Group's Seafood Calculator to find a safe serving size.) But an earlier survey by Rutgers University found that people who eat sushi weekly-particularly types that are higher in mercury like tuna-are at risk for excessive mercury poisoning. If you don't want to dial it back, at least opt for lower-mercury rolls like eel, crab, salmon, or kelp. (Or skip the sushi restaurant altogether and learn How to Make Homemade Sushi Rolls, subbing in any low-mercury fish or faux fish you desire.) And if you're pregnant or thinking of trying to get pregnant, avoid ahi tuna altogether in favor of fish that are lower in the heavy metal and high in healthy omega-3s, like salmon or sardines, recommends the Environmental Working Group.