Associations of body mass index and metabolic health with stroke risk in a large prospective cohort with time updated covariates

Why body size and health markers matter for the brain

Many people know that extra weight can strain the heart, but fewer realize that it can also affect the risk of stroke, a sudden loss of blood flow to the brain. This study from northern Sweden followed more than one hundred thousand adults for decades to explore how body mass index, a common measure of body size, and everyday health markers like blood pressure and blood sugar relate to stroke over time. The findings help answer a question that concerns many people carrying extra pounds: can someone be overweight but still “healthy” when it comes to stroke risk?

Following health and strokes over many years

The researchers drew on a long running health project in two northern Swedish regions. Participants attended one or more health examinations between the mid 1980s and 2020s, where staff measured height, weight, blood pressure, blood fats, and blood sugar, and asked about smoking and education. These checkups were repeated for many people, allowing the team to track changes in weight and health markers over time. Stroke cases were identified by linking participants to national stroke and hospital registers, and each person was followed from their first checkup until stroke, death, or the study end in 2024.

Sorting people by weight and metabolic health

Body mass index was grouped using World Health Organization cutoffs: underweight, normal weight, overweight, and obesity. Metabolic health was defined in simple terms: people with high blood pressure, high cholesterol, raised blood sugar, or diagnosed diabetes were classed as having poor metabolic health, while those without these problems were considered metabolically healthy. By combining these two ideas, the researchers could compare, for example, metabolically healthy people with obesity to metabolically healthy people of normal weight, and see how their stroke risk differed over time.

What the numbers revealed about stroke risk

Over more than 2.6 million person years of follow up, 7,493 participants had a stroke. When the team examined body mass index as a continuous scale, they found a U shaped pattern: stroke risk was lowest for people in the low normal range and rose at both very low and higher body sizes. After taking age, sex, smoking, education, and calendar period into account, people who were overweight still had about a 14 percent higher risk of stroke than those of normal weight, and people with obesity had about a 36 percent higher risk. Underweight was also linked to higher risk, although fewer people fell in this group, making estimates less precise.

The combined impact of weight and metabolic health

Poor metabolic health on its own was a strong warning sign for future stroke. Yet body size added extra information beyond these markers. Compared with metabolically healthy people without obesity, those with both obesity and poor metabolic health had the highest risk of stroke. People with poor metabolic health but no obesity also had clearly raised risk, and even metabolically healthy people with obesity had a noticeably higher risk than healthy normal weight peers. The link between obesity and stroke was stronger at younger ages and weakened in older adults, suggesting that excess weight in early and middle adulthood may be particularly harmful for the brain.

What this means for everyday prevention

For a lay reader, the central message is that both body size and common clinic measures like blood pressure and blood sugar matter for stroke risk, and that extra weight is not harmless even when these numbers look acceptable. The study suggests that there is no fully “healthy” form of obesity when it comes to stroke. Rather than focusing only on cholesterol or blood pressure, prevention efforts should also support healthy weight and lifestyle, especially in younger and middle aged adults, to help lower the chance of stroke later in life.

Citation: Hultstrand, O., Jernberg, A., Darehed, D. et al. Associations of body mass index and metabolic health with stroke risk in a large prospective cohort with time updated covariates. Sci Rep 16, 16590 (2026). https://doi.org/10.1038/s41598-026-55119-2

Keywords: stroke risk, body mass index, obesity, metabolic health, cohort study