How to read a health headline (without a PhD)

Health news is full of big numbers. Some are solid, some are shaky, and most need a little context. Five questions will get you most of the way there.

1. Was it an experiment, or an observation?

Link to this section: 1. Was it an experiment, or an observation?

Most of what we know about exercise and long life comes from observational studies: researchers measure people’s activity and follow what happens to them. These can show strong links, but not proof. People who walk a lot may already be healthier, and illness can make people walk less, not the other way round.

In a randomized trial, a coin toss decides who gets the treatment. That makes the groups alike in every other way, so differences are more likely caused by the treatment. Trials are harder and more expensive, which is why there are fewer of them.

2. Relative or absolute?

Link to this section: 2. Relative or absolute?

A real example: in the Generation 100 trial, Norwegian researchers randomly assigned 1,567 people aged 70 to 77 to five years of twice-weekly high-intensity interval training, moderate exercise, or following the usual activity guidelines.

A headline could say the interval group had “37% lower risk of death.” That is the relative difference. The absolute difference is 1.7 fewer deaths per 100 people over five years. Both are true, but they feel very different. And in this case, the study was too small to be sure the difference wasn’t chance.

3. How big, and how long?

Link to this section: 3. How big, and how long?

Bigger studies that follow people for longer give more reliable answers. Look for the number of people and the years of follow-up. Pooled analyses of many studies, called meta-analyses, are usually more trustworthy than a single study.

4. Who was studied?

Link to this section: 4. Who was studied?

Results may not apply to everyone. In Generation 100, most participants were already healthy and active, and many in the comparison group chose to exercise hard on their own, which narrowed the difference between groups.

5. Does it fit with everything else?

Link to this section: 5. Does it fit with everything else?

One surprising study rarely overturns decades of evidence. When dozens of studies in different countries point the same way, like the link between fitness and long life, that consistency is itself strong evidence.

This article is for general education and is not medical advice for any individual.