Women are nearly twice as likely to experience anxiety as men, a global review reveals.
Its authors from Cambridge University say that as well as women, young people under 35 and those with health problems are particularly affected.
They estimate that four in every 100 people have anxiety.
The review of 48 published pieces of work says more research is needed to find out which other communities are at high risk.
Published in the journal Brain and Behavior, the global review found that more than 60 million people were affected by anxiety disorders every year in the EU.
North America is thought to be worst affected, with eight in 100 people having anxiety, and East Asia least affected (three in 100).
Although the proportion of people suffering with this mental health problem stayed fairly constant between 1990 and 2010, the authors said it was a problem which was rarely researched, unlike depression.
Review author Olivia Remes, from the department of public health and primary care at the University of Cambridge, said anxiety disorders could make life extremely difficult.
"There has been a lot of focus on depression - which is important - but anxiety is equally important and debilitating; it can lead to the development of other diseases and psychiatric disorders, increase the risk for suicide and is associated with high costs to society."
She added: "It is important for our health services to understand how common they are and which groups of people are at greatest risk."
What is an anxiety disorder?
It's feelings of worry, fear and unease which persist for a long time and become overwhelming, affecting everyday life.
Physical sensations such as raised blood pressure, feeling nauseous and disrupted sleeping are common.
At this point, it becomes a mental health problem and a diagnosis of a specific anxiety disorder can be given.
Globally, women were found to be twice as likely to experience anxiety as men.
Ms Remes said this could be because of hormonal fluctuations or because women are more prone to stress in general, or because of their traditional role of caring for the young.
The review said people with a chronic health condition were at particular risk, "adding a double burden on their lives".
For example, 32% of people with multiple sclerosis have an anxiety disorder and 15 to 23% of cancer patients are affected.
The review noted that data on anxiety was particularly lacking in some populations, such as indigenous cultures, and some communities, like drug users, sex workers and lesbian, gay and bisexual people.
Pregnant women were also found to be particularly prone to obsessive compulsive disorder (OCD) - a form of anxiety disorder - before and immediately after the birth of their baby.
Before you begin any treatment you should discuss your options with your doctor.
There are self-help books and online courses that can offer ways to manage your anxiety.
Your doctor may also recommend that you avoid too much caffeine and alcohol, and stop smoking.
Taking regular exercise may also help you relax.
You may be advised to try psychological treatment, such as cognitive behaviour therapy (CBT) or mindfulness. CBT aims to challenge negative thoughts and behaviours, while mindfulness encourages the individual to focus on the here and now.
There are also different drug treatments that your doctor may prescribe.
Stephen Buckley, head of information at mental health charity Mind, said anxiety was one of the most common mental health problems in the UK.
"Many people wait too long before seeing their GP, discounting social anxiety as just day-to-day stress.
"But it's not the same as being 'a bit shy' and it's important to seek help as soon as possible if you feel like your anxiety is interfering with your ability to do the things you normally would."