(Health.com) -- Let's be honest: Many of us -- OK, most of us -- weren't exactly paragons of health in our youth. And we can't help wondering: Will those margaritas, junk-food binges, forgotten condoms, or even that one bong hit eventually come back to haunt us?

"I cringe when I think of the abuse I heaped on my body when I was younger --smoking, drinking, using tanning beds," says Stephanie Marchant, 43, a marketing consultant in Woodstock, Georgia. "I'd like to try to repair the damage, but I wonder how much I can do at this point. Is the damage already done?"

To find out just how worried Marchant and the rest of us should be, we took our fears straight to the people who should know: health experts who've studied the long-term effects of those youthful bad habits. What they say may surprise -- and reassure --you.

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In your past: You loved to party -- with a margarita in your hand.

It's no big deal if ... you overdid it once in a while in college or your 20s, but you're a moderate drinker now. One can have a drink every day without dire consequences. The liver has a wonderful ability to regenerate, so unless you inflicted years of damage, you're probably OK.

It might matter if ... you used to binge nightly (defined as four or more drinks in about two hours), or you're still having multiple drinks each day. "Binge drinking can kill neurons in the brain, affecting decision-making, learning, and memory.

The more you do it, the greater the risk," says Dr. Fulton Crews, Ph.D., director of the Bowles Center for Alcohol Studies at the University of North Carolina at Chapel Hill School of Medicine. Plus, because the liver is responsible for breaking down alcohol and clearing it from the body, heavy drinking -- more than a few drinks a day for over 10 years -- can cause hepatitis, cirrhosis, and liver cancer. Experts also say that more than a drink a day increases the risk of breast cancer.

To start fresh:

Get an hour of aerobic exercise most days of the week (brisk walking counts). It can help new neurons grow in the brain, which may reverse some damage from past alcohol abuse.



Drink in moderation -- no more than one a day. "If you're more saintly now, you've probably started to reverse your cancer risk," says Dr. Joel B. Mason, M.D., professor of medicine and nutrition at Tufts University.

Eat a healthy diet. If you were a heavy drinker, avoid high-protein diets, which can be especially hard on your liver. Also, get enough B vitamins -- such as folate (in leafy greens, beans, and whole grains), which research has shown may lower drinkers' risk of breast cancer.

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In your past: You lived on fast food.

It's no big deal if ... you ate a couple of fast-food meals a week in your teens and 20s. A little junk food won't hurt you long term.

It might matter if ... you hit the drive-through nightly. If you spent years eating as if the basic food groups were burgers, fries, and pizza (loaded with saturated fat), or snacking on nothing but store-bought cookies and chips (trans-fat heavy), it's safe to say you ate too much bad fat.

"A high-fat diet can pose a serious risk for heart disease," says Dr. John P. Foreyt, Ph.D., director of the Behavioral Medicine Research Center at Baylor College of Medicine. "Fortunately, studies show that you can reverse arterial damage if you change your diet and get more exercise, and even small changes can have significant effects."

To start fresh:

Make healthy substitutes. "Don't go cold turkey," Foreyt suggests, "because it will only increase your cravings for these foods." Instead, step back gradually. If you drink whole milk, for instance, work down to 2 percent, then 1 percent, then skim.

Have your cholesterol checked. If it's high, take steps to lower it: Follow a high-fiber diet rich in fruits, vegetables, and whole grains, and low in saturated fat and trans fat; and work out regularly, with at least 30 minutes of aerobic exercise most days of the week. If your levels are still too high, your doctor may prescribe statins or other cholesterol-lowering drugs.

Check your BMI. (An easy calculator is at NHLBISupport .com/bmi.) If it's above 25 and you're overweight, try to drop some pounds. Losing even 5 percent of your body weight can lower your risk of diabetes, says Joyce Lee, M.D., MPH, assistant professor of pediatric endocrinology at the University of Michigan.

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In your past: You spent your summer weekends soaking up the sun sans SPF.

It's no big deal if ... you've been religious about SPF 30 for the past decade or more. You still damaged your skin (sorry!), but you're certainly better off than those who've never given up unfiltered sun worship.

It might matter if ... you tanned for years (or still do). The sun's ultraviolet rays not only erode collagen and elastin (the skin's structural supports), causing premature signs of aging, but also cause mutations in its cells' DNA. Although most damaged cells die, some can replicate, giving rise to skin cancer.

"The generation of women who grew up in the '60s and '70s, before the safe-sun message was out there, may get more skin cancer than any in history," says Dr. Ellen Marmur, M.D., author of "Simple Skin Beauty" and chief of dermatologic and cosmetic surgery at The Mount Sinai Medical Center in New York City. And, she says, if you went to tanning salons, your risk may be especially high:

Even a few sessions can increase your risk of melanoma. "If you regularly find new moles and have had pre cancerous growths called actinic keratoses, those are signs that your body hasn't responded well to the sun," says Dr. Jason Reichenberg, M.D., associate program director for the University of Texas Southwestern Department of Dermatology in Austin.

To start fresh:

Protect your body every day by applying a shot-glass-size amount of sunscreen, SPF 30 or higher. Even if you're just starting now, it can pay off big-time by preventing pre cancerous moles from becoming cancerous.



Check your skin monthly for suspicious moles -- ones that are asymmetrical, have irregular or indistinct borders, or are more than one color or an unusual color (black, blue, red, or white). Don't forget your scalp, privates, and the bottom of your feet, because melanoma can turn up in places the sun rarely hits. Moles that bleed, itch, or are painful are red flags, too. If you're concerned, call your dermatologist and tell the receptionist you found a potential skin cancer so he or she will get you in ASAP -- important because if you catch skin cancer early, the better your prognosis is.

See your dermatologist every two years -- more often if you have factors that put you at increased risk of skin cancer, such as a family history. If you have precancerous changes, ask about the new generation of prescription creams that can help the skin repair those lesions. As for wrinkles and age spots, you can turn back the clock with everything from prescription Retin-A to bleaching creams. "Different skin types respond to treatments and formulations differently," Reichenberg says. A dermatologist can evaluate your skin for the most effective approach.

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In your past: You used to be a social smoker.

It's no big deal if ... you only smoked, say, 10 cigarettes a week for a few years (at parties, over coffee with friends, or when you were super-stressed).

It might matter if ... you were a heavier smoker -- smoking a pack a day for 10 years or more. Your lungs could be significantly impaired now -- enough so you might notice you can't breathe easily during exercise or you're more prone to pneumonia or bronchitis. "Your risk of smoking-related illnesses, such as emphysema, heart disease, and lung cancer, is related to how much you smoked and how long, " says Dr. Norman Edelman, M.D., chief medical officer of the American Lung Association.

There may also be damage to your arteries, increasing your chances of heart disease and stroke, though the longer you're smoke-free the more your body will heal. For instance, even if you smoked like a chimney, your elevated risk of heart disease and stroke decreases dramatically in the first 15 years after quitting, and your risk of lung cancer returns to nearly that of a nonsmoker. And, yes, if you lived with a smoker or spent lots of time in smoky bars, you increased your risk of smoking-related illnesses, including heart disease and cancer -- but not as much as if you actually smoked yourself, Edelman says. And once you've left those smoky environments behind, your risk should drop toward normal after 10 to 15 years.

To start fresh:

Talk to your doctor about any respiratory problems, like trouble breathing, catching your breath, or chronic coughing. She may suggest a pulmonary-function test to rule out serious issues -- which would go a long way toward calming your fears, too.



Do an hour of aerobic exercise most days of the week. "Aerobic exercise strengthens your heart and muscles, which helps compensate for any impairment in the lungs," Edelman says.

Eat plenty of antioxidant-rich leafy greens (like spinach, kale, and Swiss chard), as well as fiber-rich foods. Antioxidants are good for the lungs, and French researchers have found that people who eat lots of fiber have a lower risk of developing chronic lung disease, regardless of their smoking history.

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In your past: You had a one-night stand (or two) without protection.

It's no big deal if ... it was a very rare event. True, even a single heat-of-the-moment lapse is enough to pick up a sexually transmitted infection (STI) --including HIV -- but the odds are very low if you've since tested negative.

It might matter if ... it happened often. The more partners you had -- especially if you were careless about using condoms -- the greater your risk of a STI, and you might not have even known you were infected.

Chlamydia and gonorrhea are often asymptomatic and left untreated can cause pelvic inflammatory disease, a leading cause of infertility and ectopic pregnancy. Genital human papillomavirus (HPV), the most common STI, is also spread through unprotected sex. The body clears most cases on its own within two years, but certain types can linger and cause genital warts or even cervical cancer.

And before age 20 or so, your cervical cells were more susceptible to infection. You could also have contracted genital herpes, usually caused by herpes simplex virus type 2, which often produces few or no symptoms. About 26 percent of women in their 40s are infected, according to Dr. Jeanne Marrazzo, M.D., associate professor of medicine at the University of Washington. "It can cause periodic outbreaks of genital sores, but the greatest risk is during childbirth, when an active infection can be transmitted to your newborn, with potentially fatal consequences." Herpes also makes you more susceptible to HIV infection if you have sex with an infected partner.

To start fresh:

Ask your doctor for blood tests to check for STIs to give you peace of mind. Some doctors may also offer a rapid HIV test that detects antibodies in your saliva and can provide results in as little as 20 minutes.

Get regular Pap smears, which can detect precancerous changes to your cervix. Cervical cancer is so slow-growing that it might not show up till your 40s or 50s, even if you were exposed to the human papillomavirus years before. If you have a normal Pap test three years in a row, you can wait three years for your next one--unless you have symptoms like bleeding between periods or unexplained discharge.

Be frank with your obstetrician about your sexual history if you're pregnant or planning on getting pregnant. It's important for the doctor to know if you have herpes, so she can be on the lookout for signs of an active outbreak during delivery and do a C-section if she sees something suspicious.

Use condoms regularly if you're with a new partner, even if you're in your 30s, 40s, or beyond, because you can get, or spread, an STI at any age, Marrazzo says.

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In your past: You smoked pot.

It's no big deal if ... you did it once in a while. A bong hit now and again isn't a worry (phew!).

It might matter if ... you lit up regularly. "If you smoked marijuana daily for 20 years or so, you may develop permanent respiratory problems, like chronic cough and shortness of breath," says Dr. Harold Kalant, M.D., Ph.D., professor emeritus in pharmacology at the University of Toronto.

Marijuana may also increase the risk of lung cancer, but long-term use -- 10 years or more -- seems to be the most damaging. And daily users might be left with mild but lasting memory problems.

To start fresh:

Get an hour of aerobic exercise most days of the week -- it's good for your lungs, as well as your brain.

In your past: You binged, then starved -- that is, did some extreme dieting.

It's no big deal if ... you gained and lost more than 10 pounds a couple of times but have since maintained a more or less stable weight for the last decade or two.

It might matter if ... you lost and regained more than 10 pounds many times over the years. Those feast-or-famine cycles may have subtly slowed your metabolism and diminished your ability to recognize your body's hunger and satiety signals -- making it easier for you to gain weight now, says Dr. Cynthia Bulik, Ph.D., director of the University of North Carolina Eating Disorders Program and author of "Crave: Why You Binge Eat and How to Stop."

Frequent yo-yo dieting can also up your risk of gallstones and may weaken your immune system. Researchers found that repeated weight loss seems to decrease the activity of natural killer cells, which help your body fend off illnesses. The good news: Women who maintained the same weight for five or more years had 40 percent greater natural killer cell activity than those whose weight had been stable for less than two years.

To start fresh:

Lose weight gradually, so you have the best shot at keeping it off. Gradual weight loss also reduces the risk of gallstones. Avoid extremely low-fat diets (some fat is good; it stimulates the gallbladder to contract and empty). And get plenty of fiber and calcium, which may lower the risk of gallstones, as well.

Do an hour of aerobic exercise most days of the week. It will help you keep your weight in check and may blunt the negative effects of weight loss on your immune function.

Manage your stress with your favorite relaxation method -- whether it's taking a walk, doing yoga, or reading. "Those with a history of bingeing are more likely to relapse when stressed," warns Dr. Mary Boggiano, Ph.D., associate professor of psychology at the University of Alabama at Birmingham. So that knitting project or book club isn't just good for your mind; it can also help you maintain a healthy weight.

Copyright Health Magazine 2011