“Wait an hour after eating before swimming.” “Feed a cold, starve a fever.” “Drink eight cups of water a day.” “Don’t stress—it’ll turn your hair gray!” Many of us have heard at least one, if not all, of these sayings, but which are true and which should we disregard?

• Do we need to wait an hour after eating before we jump into the pool?

Most moms would probably say that we should wait 30 minutes, arguing that when we eat, blood rushes to aid our digestive tracts (Duke University Health System 2010). With all of that blood in our bellies, how will our legs and arms stay afloat while we swim?

Though it is possible to feel tired after indulging in a heavy meal (Mayo Clinic Staff 2011), it’s probably not necessary to wait an hour for digestion’s sake. Our arms and leg muscles have enough blood to allow us to swim (Duke University Health System 2010).

• Another food-related adage revolves around our bodies’ abilities to fight infection. Is there any truth in “feed a cold, starve a fever”?

When we’re sick, we sometimes lose our appetites—regardless of whether we’re fighting a cold or a fever—because our bodies are so focused on fighting the pathogens. But if you’re hungry, you should eat—particularly foods that are high in antioxidants (e.g., cantaloupe, spinach) and help boost your immune system (Bishop 2010; WebMD 2012).

Food also provides about 20% of our daily water intake, helping to fight dehydration, which can be caused by sweating or excess mucus production—both symptoms of the flu (NYU Langone Medical Center 2013). So though the “feed a cold” part isn’t too farfetched, it’s never a good idea to starve.

• Should we drink eight glasses of water every day?

Our bodies are approximately 60% water, using it to flush toxins, carry nutrients, and coat our ears, noses, and throats (Mayo Clinic 2011). But our water needs vary, depending on where we live (those who live in warmer climates probably lose more water through sweat), how much we exercise, and our overall health (Mayo Clinic 2011; Valtin 2002).

That said—rare though it may be—it is possible to consume too much water (Mayo Clinic 2011). Our thirst is typically a good indicator of whether we should drink (Valtin 2002). The average man should consume about 13 cups of fluid (i.e., not just water) daily and the average woman about nine cups (Mayo Clinic 2011). Even caffeinated beverages (e.g., tea, coffee, soda), often misconstrued as diuretics, contribute to our bodies’ hydration levels (Valtin 2002).

• We often hear that stress can cause our hair to turn gray. Even the president’s hair is a constant topic of concern in the media. But do stress levels really affect our hair color?

To understand why our hair turns gray, we must first comprehend the origin of our natural hair colors. Natural hair colors are a result of the distribution, type, and amount of a pigment called melanin. As we age, our genes tell our bodies to produce less melanin, turning our hair gray, then white (Saling 2011). Of course, the age at which our hair turns gray depends on our genes.

Though no direct evidence exists to prove that stress causes gray hair, some of the adverse effects of physiological stress—loss of sleep and appetite—can contribute (Saling 2011; LOC 2012).

Though many “urban legends” contain partial truths, we can’t believe everything we hear. And as always, it’s best to check with your doctor before you make any decisions about your health!

Do you have a question for the Health Wise column to answer? Send an e-mail tostreker@nsta.org.

Acknowledgment

Sincere thanks to Lawrence J. Cheskin, associate professor of health, behavior, and society and director of the Johns Hopkins Weight Management Center at Johns Hopkins University in Baltimore, Maryland, for reviewing this column.

References

Bishop, E. 2010. Myth or fact: Feed a cold, starve a fever. Duke University Health System. http://bit.ly/cwjp9A

Duke University Health System. 2010. Myth or fact: Wait 30 minutes after eating to go swimming. http://bit.ly/cbRV7e

Library of Congress (LOC). 2012. Why does hair turn gray? http://1.usa.gov/6SGuQ2

Mayo Clinic Staff. 2011. Water: How much should you drink every day? Mayo Clinic. http://mayocl.in/aj2w0F

Mayo Clinic Staff. 2011. Kids’ swimming: Keep health risks at bay. Mayo Clinic. http://mayocl.in/aj2w0F

New York University (NYU) Langone Medical Center. 2013. True or false: Feed a cold, starve a fever. http://bit.ly/TPAbSq

Saling, J. 2011. The effects of stress on your hair. WebMD. http://on.webmd.com/p6AYND

Valtin, H. 2002. ‘Drink at least eight glasses of water a day.’ Really? Is there scientific evidence for ‘8 × 8’? American Journal of Physiology: Regulatory Integrative and Comparative Physiology 283 (5): R993–1004.

WebMD. 2012. Starve a cold, feed a fever? http://on.webmd.com/1Cj1