Exceptions to 5 common health rules

No one ever got sick from avoiding cigarettes or trans fats. But some of the most commonly repeated pieces of advice actually aren't meant for everyone. After all, the USDA couldn't equip its pyramid with a section just for people with celiac disease or those taking certain meds. Health recommendations are sometimes based on studies that didn't include a good cross section of the general public. So we took a look at some pieces of conventional wisdom that are truly wise for most people and asked the experts what you ought to do, just in case you're not completely average in every way.

1. Swimming is ideal low-impact cardio

Tailor it: if you have asthma

The chlorine in a pool—even if it's outdoors—can trigger an attack. In children, it may even raise the odds of developing the disorder in the first place. To be on the safe side, find a different form of exercise if you have asthma that flares up poolside, experts say; if you have a child under age 7 with allergies, don't take him to a pool with a strong smell of chlorine.

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2. Eat plenty of leafy green vegetables

Tailor it: if you take the blood thinner warfarin (Coumadin)

This drug prevents dangerous blood clots by blocking the action of vitamin K, which is needed to make clot-building compounds in the blood—but too much K in your diet can overwhelm your protection. The nutrient is especially abundant in dark green, leafy vegetables such as spinach, Swiss chard, and kale, so don't have more than one serving of any of these in a day.

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3. Drink at least 8 glasses of water every day

Tailor it: if you have any bladder issues

You might be able to avoid leaks by cutting back a bit on fluids. Ask your doctor how much you should drink each day—and don't worry if it doesn't come close to the magical "8 glass" rule. Nearly 20% of your water intake comes from food anyway, according to the National Health and Nutrition Examination Survey.

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4. Acetaminophen is the safest pain med

Tailor it: if you have a glass of wine (or any alcohol) daily

It’s well-known that acetaminophen can damage the liver in high doses, especially in heavy drinkers. But even light drinking can prime the liver for trouble, says Donald Jensen, MD, a medical advisor for the American Liver Foundation. Although 3,900 mg of acetaminophen is the recommended maximum daily dose, you shouldn't exceed 2,000 mg on any day you have even one drink.

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5. Get nutrients from whole foods, not pills

Tailor it: if you're a strict vegetarian

If you don't eat eggs or drink milk, you may need supplements to get enough vitamins B12 and D. Try 6 mcg of B12 (the amount in a typical multi). The current recommendation for vitamin D is 200 to 600 IU, depending on your age, but researchers say that needs an update: 1,000 to 2,000 IU is optimal and safe to take. And although you can get plenty of iron through a vegetarian diet, it takes planning.

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