© Maskot | Getty Images Mental health challenges are very common, and often treatable. Seeking help and approaching therapy with an open mind can make all the difference.

About 50 percent of the popu­lation will develop a mental health disorder by the age of 75, according to a large international study that also found the most common disorders differ between women and men.

The study, led by researchers at Harvard Medical School and Australia’s University of Queensland, covered a period of 20 years and involved more than 150,000 adults. Researchers examined medical records and conducted face­ to-face interviews. The study was published recently in The Lancet Psychiatry. 

Researchers found that most mental health disorders first appeared in childhood, adolescence, or young adulthood, though they can develop at any age.

The peak age of first onset was at 15 years old, while the median age of onset was 19 for men and 20 for women. Ronald Kessler, PhD, McNeil Family Professor of Health Care Policy at Harvard Medical School and one of the study’s lead researchers, suggests that investing in mental health services, with a partic­ular focus on young people, is urgently needed.

“Services need to be able to detect and treat common mental disorders promptly, and be optimized to suit patients in these critical parts of their lives,” Dr. Kessler says. “By understanding the age at which these disor­ders commonly arise, we can tailor public health interventions and allo­cate resources to ensure that appro­priate and timely support is available to individuals at risk.”

Key Findings

While the study findings suggest that most disorders develop by early adulthood, it’s important to understand that mental health chal­lenges can appear at any age. For people with mood disorders or other emotional problems for years without ever understanding what was wrong, getting a diagnosis later in life can provide precious insight into previous difficulties with employment, rela­tionships, and other facets of life. And a diagnosis at any age can lead to much-needed treatment.

In addition to narrowing down the usual age of disorder onset, the study findings also identified the most common mental health disorders and how they differ by sex. Not surpris­ingly, anxiety and depression topped the list overall.

However, for women, the three most common mental health disor­ders were depression, a specific phobia (such as claustrophobia and acrophobia), and post-traumatic stress disorder (PTSD). For men, the top three were alcohol abuse, depres­sion, and a specific phobia.

For the study, researchers analyzed data collected by the World Health Organization’s World Mental Health Survey initiative, which includes the largest coordinated series of face-to­-face interviews seeking to understand the reach of mental illness across populations.

Prevalence of Mental Illness

Despite the size and scope of this research, estimating the prevalence of mental health disorders remains chal­lenging for several reasons. Mental ill­ness is sometimes referred to as a “silent disease” because it exists on a continuum of severity, and people with “mild” depression or anxiety, for example, may never get a diagnosis, let alone seek out treatment. Individ­uals who might benefit from treat­ment may also miss out because of cultural or familial stigma around mental health or because they don’t have easy or affordable access to ser­vices and other resources.

For these and other reasons, the WHO estimates that nearly two­ thirds of people with mental illness go without treatment, and this applies to people with a range of mental health challenges. The National Institute of Mental Health (NIMH), for example, suggests that about half of adults in the United States with bipolar disor­der and 40 percent of those with schizophrenia went untreated during a one-year study period.

While it’s important for researchers, clinicians, and policy makers to have a good handle on the prevalence of mental illness, what’s most important for you and your loved ones is that you take the signs and symptoms of mental illness seri­ously. Don’t brush off noticeable changes in personality and behavior or assume such changes are passing phases or unavoidable aspects of get­ting older.

Mental health disorders are often treatable, and they don’t always require medication. You may be able to find help through talk therapy and lifestyle changes, but seeking a mental health professional to start the process is usually an essential first step. If you’re unsure about how to start, talk with your primary care doctor about any concerns you have. Ask for a recommendation for a ther­apist, and adopt the attitude that help is available if you’re willing to accept it.