This Time magazine story describes a large study that looked at survey data from Norway to determine if exercise played a role in reducing the risk of developing depression among the 22,000 participants. The story suggests that it does and, to its credit, points out that this kind of study cannot show a causal relationship between exercise and the prevention of depression.
The story is filled, however, with conditional statements about what may or may not be happening in this research. It also lacks any statements from sources independent of the study.
Independent sources provide an important counter-balance to comments from researchers directly involved with the study. Conditional statements like “may help” can also be phrased as “may not help”–more specific language helps readers understand the real benefit.
Costs aren’t a factor in this story given that the researchers are suggesting that even minimal exercise, such as walking and cycling, can lead to the decrease in depression they say that they have found. It costs nothing to walk and, aside from the cost of a bicycle, cycling is also free. Perhaps the biggest cost is a time cost–people who work long hours at sedentary jobs may have a hard time fitting this into their schedules.
The story barely passes this criterion with, “People who said they didn’t exercise at the study’s start were 44% more likely to become depressed, compared to those who exercised at least 1 to 2 hours a week.” Also, “they say, 12% of depression cases could be prevented if everyone got just one hour of exercise a week.”
But to be fully informative it’s important to put the 44% percent in absolute terms. How many people in the exercise group developed depression, and how many people in the non-exercise group developed depression?
We’ll give this N/A since the risks associated with light exercise are fairly minimal. However, we think it’s always a good idea to discuss the potential harms of an intervention. In this case, the story implies that very light and infrequent exercise provides this benefit. Does this encourage people to exercise less and to then lose out on other health benefits of more exercise? Injuries are also an issue for those going from no to some exercise.
The story explains the results of a study that “followed more than 22,000 healthy Norwegian adults without symptoms of anxiety or depression for an average of 11 years.” It also explains that, “The study could not prove a cause-and-effect relationship between exercise and the risk of depression.”
The large size and the statement that the findings aren’t causal are both indicators of the quality of the evidence.
But then the story adds, “but the authors say it strongly suggests one,” referring to a causal relationship. Studies like this one cannot prove causality and since they were based on the self-reporting of participants, their conclusions should maintain some skepticism. Add to that the fact that the story is loaded with conditional statements: “Regular exercise may prevent,” “If their hypothesis is right,” “depression cases could be prevented,” “People seemed to have mental health benefits,” “benefits of exercise are likely responsible,” “exercise may also have a role in preventing people developing depression” All of these conditional statements suggest that the evidence may or may not hold up over time.
Other factors: The study is of Norwegians. How generalizable is it? And, the self-reported exercise information was collected only at the start of the study, the amount of exercise that participants completed regularly was not assessed at any other time. The study itself is careful to say this, but the story makes it sound as if ongoing exercise was documented.
No disease mongering here.
The story doesn’t include any content from independent sources.
The study does mention that exercise, if it is proven to have a positive effect on depression, should be used along with medications and counseling in people who already have been diagnosed.
However, it does not discuss methods for preventing depression. Are there any? Even if there are none, that should be mentioned.
While it makes no statements about availability, most readers will realize that exercise, such as walking and cycling, are usually readily available.
Exercise for mental health is not a new concept. What makes this study novel is that it’s looking at exercise’s potential to prevent depression, and if that impact would be useful enough for a public health level initiative. As the study explains:
“While many agencies are keen to promote the potential mental health benefits of exercise, at present the literature is unable to provide the most basic information needed for effective, targeted, evidence-based public health campaigns concerning depression and anxiety.”
The story didn’t explain this.
The story does not appear to rely on the news release as it includes quotes from an email interview with the author. However, it did not provide any information not already found in the news release.