Think what you do today has no bearing on your sex life tomorrow, or the day after? Think again.

The plight of the typical young man isn’t the inability to have sex; it's usually the inability to find someone to have sex with.

Fact is, though, if you think you don’t have to worry about erectile dysfunction (ED) until your hair starts to turn gray, think again. Even in your early 20s, chances are your arteries are already undergoing changes that may culminate years from now in ED.

Fundamentally, erection depends on blood flow into the penis. The more blood, the more reliable and firm your erection. But when arteries become narrowed by cholesterol-rich atherosclerotic plaque deposits, less blood flows into the penis and erections wilt. This becomes apparent by the time a man hits 50.

Harvard researchers tracked 31,742 middle-aged men for 14 years and found that ED is strongly linked to lifestyle factors that spur the growth of atherosclerotic plaques: smoking, obesity, heavy drinking and lack of exercise.

But plaques don’t pop up out of nowhere when you hit 50. They start to develop in childhood. Autopsies of American males killed in their late teens and 20s in accidents or in war consistently show the beginnings of atherosclerotic plaques, which means the beginning of ED.

Meanwhile, a healthy lifestyle keeps blood flowing freely through the arteries and preserves erection function. Healthy living doesn’t mean you’ll have the ability of legends at 90. But if you want to function sexually on Social Security, you’d be smart to adopt a healthy lifestyle now. Here’s how:

Get Regular, Moderate Exercise
Exercise is crucial for arterial health and blood flow into the penis. Exercise lowers cholesterol, which minimizes the deposits (plaques) on artery walls that narrow them and reduce blood flow. A study of middle-aged men at the University of California, San Diego, shows that as regular, moderate exercise increased, erections become more reliable. ED-preventive exercise doesn’t require extreme sports, but rather the equivalent of brisk walking for about an hour a day. “No question about it,” says Hank Wuh, M.D., author of Sexual Fitness. “Regular exercise improves erection function and sex.”

Eat Less Meat, Cheese and Junk Food, and More fruits and Vegetables
Meat, cheese and junk food are high in saturated (animal) fat. Like cholesterol, this fat narrows the arteries, limiting blood flow to the penis. Fruits and vegetables, on the other hand, contain antioxidant nutrients that minimize plaques and improve arterial blood flow. Italian researchers identified 65 men with incipient ED and asked half of them to eat less meat and cheese, and more fruits and vegetables. After two years, those who maintained a high-fat diet continued to have erection difficulties. But those who increased their fruit and vegetable consumption reported significantly less ED.

Lose Excess Weight
According to the Harvard study of middle-aged men, obesity is strongly associated with ED, and weight loss improves erection function. That’s not surprising. As we’ve seen, exercise and a diet low in saturated fat improve erections. They are also cornerstones of weight control. Studies at the Duke University Diet and Fitness Center show that as men lose weight and become more physically active, they report better erections.

Stop Smoking
Cigarettes greatly accelerate the growth of artery-narrowing plaques. A study at the New England Research Institute in Watertown, Mass., shows that smoking almost doubles risk of ED. Australian epidemiologist Christopher Millett, Ph.D., says, “Health promotion programs should use the link between tobacco and ED to help convince men to quit smoking.”

Manage Your Stress
Many young men feel like they have heavy weights on their shoulders. In one recent survey, 60 percent of Americans said they feel they’re “under significant stress” at least once a week. And since the stock market crash last fall, ComPsych, the nation’s largest employee-assistance program, reports that requests for psychotherapy have surged 40 percent.

The biological result of this emotional stress: the release of two hormones (cortisol and adrenaline) that constrict arteries, reducing blood flow into the genitals.

The erection-firming antidote is an ongoing stress-management program. Proven stress relievers include exercise -- aerobic or non-aerobic (e.g., yoga) -- meditation, music (playing or listening to), massage, laughter, hot baths, gardening, caring for a pet, visualization (of relaxing scenes) and quality time with friends, family or a lover. Incorporate one or more into your daily life, or even better, combine them: Exercise with friends or bathe with your girlfriend, for instance.

Bottom line: Couch potatoes are on a one-way trip to ED. But if you get off the sofa, work out and switch from Big Macs to big salads -- with low-fat dressing, of course -- you’re much more likely to maintain firm, reliable erections as you get older and to enjoy satisfying sex.

Photo Credit: Meghan Holmes

You’ve seen commercials that feature athletes grunting through pain as if it’s a virtue. You’ve watched sports icons lead their teams to unbelievable comebacks on their seemingly inexhaustible shoulders. You’ve seen veins popping on the grimacing faces of those on “World’s Strongest Men” and Tour de France riders alike.

It’s not just macho to push yourself to the limit -- it’s considered cool. But how do you know if you’re about to take your body beyond that limit and into dangerous territory? Especially in hot weather, there are risks you should you know about. As long as you can read your body’s signs, you can prepare for pushing it without going over the top. Here, your body’s warning signs and what to do about ‘em:

Warning 1: You Stop Sweating
When doing cardio, your biggest risk is overheating. “If you stop sweating, you’re in danger of heatstroke -- which can kill you,” warns Clint Phillips, a certified strength and conditioning specialist.

What to do: In such a case, “Stop working out immediately, hydrate and cool off. Go somewhere air-conditioned, splash water on you, get in front of a fan, use an ice pack on your head.” Avoid overheating when you’re training outside in hot or humid weather by going out in the morning or evening for more effective, less risky workouts.

Warning 2: Your Urine Isn’t Clear
Tom Seabourne, Ph.D., an exercise physiologist and holder of four ultradistance cycling world records, recommends that you check your hydration levels via your urine color -- ideally, it’s clear. The darker (yellow) it gets, the closer you are to dehydration.

What to do: Go-to drinks should contain electrolytes with essential elements like sodium, potassium and magnesium. While sports drinks can be a boon for hot outdoor workouts, Phillips urges that you avoid energy drinks, which may push your heart rate too high. Oh, and water’s good!

Warning 3: Your Resting Heart Rate Is High
Keep abreast of your resting heart rate, which you can check after a good night’s sleep. “If you wake up and your resting heart rate is consistently 10 beats above your regular resting heart rate, that’s a red flag,” says Seabourne. It indicates that the body is in an overtrained mode and is not sufficiently recovered, even after a night’s rest. This can be due to a very strenuous cardio workout or even a grueling strength training session.  According to Greg Haff, Ph.D., an exercise physiologist at West Virginia University, higher repetition schemes -- such as 20 ser set -- can take four times as long to recover from than lower rep sets, such as five. If summer heat is involved, fatigue can be even greater, making recovery time longer.

What to do: During cardio workouts, make sure you use a heart rate monitor. Phillips advises that you never go over 90 percent of your maximum heart rate. (This can be calculated by subtracting your age from the number 220. To calculate 90 percent of that, multiply by 0.9.) And on days when you wake up with a resting heart rate that is higher than normal, your body is telling you that it needs more recovery. Listen and take the day off.

Warning 4: You’re Still Sore
For strength training, soreness that lasts more than a day or two usually means overtraining. Other symptoms include a lingering sense of lethargy, achiness, almost flu-like symptoms, a lack of motivation to train and even irritability. “If you can't lift as much weight or do as many reps [as you did the week before], you are probably overtraining,” says Phillips. And pain is only normal when it is throughout the whole working muscle, he adds, but pain in a joint or isolated in one small spot in a muscle means something’s wrong.

What to do: Get your z’s. Says Seabourne: Seven to eight hours of sleep is needed for an adequate release of growth hormone to build and repair muscle. When working out, err on the side of intensity over volume. Phillips says a couple of heavy sets for each muscle group is plenty. As “for cardio, I'd rather have someone do 20 to 30 minutes of high-intensity intervals than an hour of lower intensity work.” Also, consider working out with a partner, who can keep an eye on you (and vice versa).