The United States had a record 4.3 million births in 1957, which translates into a big bunch of baby boomers who are facing their 50th birthdays this year.

If you’re thinking this is the beginning of the end when it comes to your enjoyment of good health, you’re buying into misconceptions about the aging process.

Here are some myths about your body and aging:

You’re going to lose your mental faculties

First, the sobering news: Nearly half of all Americans over 85 suffer from Alzheimer’s disease. Now, the encouraging news: There are things you can do to minimize your chances of losing big chunks of your brain power as you age.

Start with what you’ve been putting in your mouth. Several studies published in the Archives of Neurology and other medical journals determined people who consume foods high in fat, saturated fat and cholesterol have at least double the risk of developing Alzheimer’s in the future.

Try to focus more on foods that are plant-based, such as whole grains, fruits, vegetables, seeds and nuts. These foods will supply your body with lots of fiber and antioxidants, which help to keep your arteries unclogged and ready to deliver an abundant supply of blood to the brain.

You don’t need as much sleep as you used to

It’s not that you need less sleep, it’s more like you may not be getting the kind of sleep you need to feel truly rested and refreshed.

Older adults need to get seven to nine hours of sleep per night, just like young adults. But older people have a tendency to have more trouble falling asleep and staying asleep than when they were younger, according to the National Sleep Foundation.

Research on the sleep habits of older Americans shows a general decline in REM or deep sleep and a rise in episodes of waking up during the night. Studies indicate physical and mental illnesses and the medications used for treatment can be reasons for many of the sleep disturbances. If you’re having trouble sleeping, find out from your doctor what you can do about it.

In the meantime, try to stick to a regular schedule. Go to bed and get up at about the same time every day. Napping is good, but you may find yourself staying awake at night if you tend to nap during the late afternoon or early evening.

You have to give up running or jogging

Unless years of hitting the pavement have damaged your knees and joints, you can keep on jogging or running to your heart’s content.

“It’s possible to continue to run until they plant you in the ground,” says Scott Fisher, an exercise physiologist, director of the Fitness Center at Fairleigh Dickinson University in Teaneck, N.J., and an avid runner himself.

Yes, these are higher-impact activities, but you shouldn’t have to quit, as long as you’ve been running or jogging in a way that’s friendly to your body. Just don’t think you’re invincible.

“Listen to your body and take care of aches and pains before they become chronic injuries,” says Fisher. “When you experience an ache or pain, modify your exercise regime and take time off to make sure you’re appropriately recovered and your body has had an opportunity to heal itself up.”

You may also want to adjust your running regimen as you get older.

“As people get older, they might find it more comfortable for them, instead of running five or six days a week as they did in their 30s, to cut back and run three or four days and do cross training a couple of days, like swimming or cycling, which aren’t as stressful on the joints,” Fisher says.

It’s too late to start an exercise program

There’s a growing body of evidence that shows exercise is just as important for the health and well-being of older people, including the elderly, as it is for younger people.

One large-scale study that followed more than 50,000 alumni from the University of Pennsylvania and Harvard College for 40 years found death rates fell in direct proportion to how many calories participants burned each week.

“Almost invariably, the more active they were, the longer they lived,” writes John Robbins, who referenced the landmark College Study in his book, “Healthy at 100: How You Can – at Any Age – Dramatically Increase Your Life Span and Your Health Span” (Random House, $25.95).

Exercise can lower your blood pressure and your cholesterol, increase your endurance and even help you sleep better. You can start by working yourself up to a 30-minute brisk walk five days a week.

But get a checkup from your doctor first to be sure there are no underlying medical issues you would need to seriously consider before embarking on a fitness regimen.

You say goodbye to your muscle strength

This little statistic could send you running for the nearest dumbbell: Most adults lose about a half-pound of muscle per year after age 20, according to the American Council on Exercise. But you can reverse a significant amount of that loss by strength training, which everyone, at just about any age, can start doing. Of course, you need to check with your doctor first to ensure you’ll be safe while exercising this way.

One study found that even nursing home residents as old as 98, many of them with chronic conditions, experienced significant increases in muscular strength after just a few months of strength training. One of the huge benefits of strength training is it builds muscle mass, which can transform your body into a more efficient fat-burning machine.

You’re going to need a hearing aid

Not everyone, of course, experiences hearing loss as part of the aging process. About a third of Americans ages 65 to 74 have hearing problems and about half of those 85 and older have hearing loss.

But there have been a growing number of media reports and warnings issued by health experts during the past few years that nearly half of U.S. boomers are experiencing some degree of hearing loss and at a more rapid pace than previous generations. Once it occurs, hearing loss is irreversible.

But you can protect yourself from experiencing hearing loss by knowing that exposure to noise levels above 85 decibels for more than 15 minutes can result in loss of hearing. The average rock concert is 115 to 120 dB, according to the Ear Foundation. Other noises that usually register above 85 dB are from such sources as lawnmowers, vacuum cleaners, musical concerts (aside from rock events) and motorcycles. Protect yourself by wearing earplugs or ear muffs.

Sources: “Healthy at 100: How You Can – at Any Age – Dramatically Increase Your Life Span and Your Health Span” (Random House, $25.95); National Institute on Aging, part of the National Institutes of Health; National Sleep Foundation; National Women’s Health Resource Center (www.healthywomen.org); “Menopause for Dummies” (Wiley, $21.95); www.dukemednews.duke.edu; www.lsuagcenter.com; Ear Foundation; “Defying Age: How to Think, Act and Stay Young” (DK Publishing, $25).