A Harvard University research team studying the effects of low testosterone and its links to depression found that during any given year, approximately 8 percent of men over 30 will suffer a serious bout of depression [source: Cromie].
But depression doesn't always have a physical cause, nor does it always express itself through classic symptoms like a loss of motivation, sadness or lack of energy. Depression in men can also manifest through increased risk-taking behavior, anger and aggression, or alcohol abuse [source: Zamora]. It can also be labeled as a midlife crisis.
Though a midlife crisis is traditionally thought of as affecting older men, a UK study has shown that men in their mid-30s can certainly fall prone to the feelings of dissatisfaction and a greater awareness of their own mortality [source: BBC News]. The joke is that a guy simply buys a sports car to get through it, but depression and midlife crises are no laughing matter; men are four times as likely to commit suicide as women [source: Zamora]. This is thought to be because guys are less likely to consider themselves clinically depressed and therefore less likely to seek treatment.
So if you're feeling glum without an immediately obvious cause, it wouldn't be a bad idea to seek help. If your testosterone levels are normal, you could consider mental health counseling. Talk therapy has actually been shown to be as effective as prescription antidepressants for banishing the blues [source: Doheny]. And although it doesn't come naturally to guys, talking about your feelings could be the best way to ensure you're around to keep talking to your loved ones in your 40s.