On "Sunday Housecall" today, a viewer wrote in and asked, "I'm an active male in my early 40s, but recently I've noticed I don't have as much muscle strength as I used to. Should I worry?"

Chairman of the Department of Urology and Chief of Robotic Surgery at Lenox Hill Hospital Dr. David Samadi said that "male menopause" is the likely culprit.

Every year after the age of 30, men produce less and less testosterone, Dr. Samadi explained. But since it's such a gradual process, many men won't notice until they get into their 50s.

"[The] male hormone will drop gradually. That's called 'male menopause,'" Dr. Samadi said, adding that the symptoms may be a drop in sex drive, concentration and quality of sleep.

Unfortunately, he said, treating low testosterone has become a billion dollar business.

"That's a knee jerk reaction," Dr. Samadi said. "That's bad medicine and there could be some side effects."

Associate Professor at NYU School of Medicine Dr. Marc Siegel agreed with Dr. Samadi that men and women who are concerned about muscle loss or changes to their body should see a doctor.

Dr. Siegel also agreed with Dr. Samadi that men who are dealing with muscle loss should check their testosterone levels, preferably in the morning before 9 a.m. to get the most accurate reading.

"At 40, you shouldn't have the pronounced muscle loss," Dr. Siegel said. "It's too early. So if you're entering 'male menopause' at 40, that's pretty early for that. You may have a problem. Get that checked."

He added that there are other things that can cause muscle loss, such as low thyroid, a problem with the hyperparathyroid gland, steroid use, obesity, diabetes and high blood pressure.

"One of the ways to increase your testosterone? Lose weight, guys," Dr. Samadi recommended. "Vitamin D is essential to boost your testosterone. Having shellfish, oysters ... egg yolk, meat, all those will boost your testosterone ... Lack of sleep affects it so make sure you sleep well."

If you've done all of that and your body is still not making testosterone, then you may want testosterone replacement treatment, Dr. Samadi said.

Watch the clip above and get more information by checking out Dr. Samadi on Facebook.