Fact or fiction: The truth about 40 popular medical “facts”

FALSE! Carrots get their vision-boosting reputation from the chemical that gives them their orange colour: beta-carotene. Beta-carotene is converted into vitamin A, which helps your eyes see better in the dark. But the conversion process isn’t very efficient, and once you’ve taken in a certain amount, the body stops converting it. For improved eyesight, eat vegetables high in vitamin A itself, including leafy greens such as kale and spinach.

FALSE! The idea that caffeine is a diuretic that leaves your body short of fluids doesn’t hold water. In fact, studies show that coffee and tea drinkers don’t use the bathroom any more than water drinkers. A cup of coffee counts as part of your fluid intake and can actually help you hydrate.

FALSE! Following conventional wisdom and putting a spoon in the person’s mouth won’t prevent tongue swallowing, but it could harm the teeth or jaws. Instead, turn the person on his or her side to prevent choking on saliva or vomit, and cushion the head with a pillow.

TRUE! Frostbite numbs the skin, so it could be burned without your realising it if it’s next to a radiator, fire, or heating pad. Instead, immerse the area in warm water.

FALSE! The two main causes of stomach ulcers are overuse of painkillers, such as aspirin and ibuprofen, and infection from the bacteria Helicobacter pylori. Stress might make an existing ulcer worse (and having an ulcer might trigger stress), but the current science shows it isn’t a direct cause.

Try these 10 habits of people who never get stressed.

TRUE! “Too often, heart patients use their condition as an excuse to cut back on physical activity when they should be doing the opposite,” says Dr Salim Virani, chair of the American College of Cardiology’s Prevention of Cardiovascular Disease Council. Hitting the standard 20 to 30 minutes most days can help strengthen your heart. Talk to your doctor about creating a safe routine.

FALSE! The old thinking was that cholesterol in food would raise blood cholesterol levels and in turn increase the risk of heart disease. A recent study of more than 400,000 adults found that eating an egg a day increased good cholesterol and cut the risk of cardiovascular death by 18 per cent.

FALSE! It might tire your eyes in the short term, but there’s no evidence that it will do any lasting damage. When reading, position light to shine directly on the page rather than from over your shoulder to reduce glare.

TRUE! Little kids are especially prone to vomiting after coughing fits because their gag reflexes are extra sensitive, but it can also happen to adults. It usually isn’t a big deal, but if you keep puking, see a doctor.

FALSE! Recent studies haven’t found a link between cracked joints and arthritis. But some studies showed that cracking your knuckles can result in soft-tissue damage (which can cause swelling) and a decrease in handgrip strength.

Even though this arthritis myth isn’t true, these 12 health “myths” actually turned out to be true.