"Suddenly, I'm not half the man I used to be..." If the words to that Beatles song make a lot more sense to you now than they did when you heard it as a teenager, there may be more to your newfound understanding than the wisdom of years.

As men get older, testosterone levels in the body gradually become lower than in the days of your youth, when you probably felt like you had the drive and energy to tackle just about anything that came your way. Testosterone is the hormone responsible for such typically "male" characteristics as deep voices, muscle mass, and facial and body hair patterns, and a shortage can spell tiredness, low sex drive, and a slew of other effects that may make you feel old beyond your years.

Starting at the age of 30, men experience a drop in testosterone by about 10% every decade, while amounts of the hormone that are still being manufactured may not be as effective because of increased production of another hormone called SBHG. For some men, this decrease in testosterone results in a condition called andropause, which has a range of symptoms, including:

• low sex drive
• difficulties getting erections or erections that are not as strong as usual
• lack of energy
• depression
• irritability and mood swings
• loss of strength or muscle mass
• increased body fat
• hot flashes

While many men think it's inevitable, feeling "down in the dumps" is not a necessary part of getting older. While an estimated 4-5 million men in the U.S. suffer from symptoms related to testosterone deficiency, only about 5% are treated. Aside from the fact that that leaves a lot of men who simply aren't feeling as good as they should, it also puts a high number at risk for osteoporosis, or a weakening of the bones, and cardiovascular problems such as atherosclerosis, hardening of the arteries - both of which are conditions associated with low testosterone.

But there's no reason for this condition to get so many men down! Doctors can easily diagnose low testosterone with a simple blood test. If levels come back low, further testing, including more blood tests, taking a sample of tissue from the testicles (called a biopsy), semen analysis, or brain imaging may be required. Once low testosterone is diagnosed, there are a number of different treatment options.