Obesity and cardiovascular risk

Obesity is among the major modifiable cardiovascular risk factors. Its effect comes through direct mechanisms on the heart and blood vessels, but also through its frequent association with high blood pressure, diabetes, and cholesterol abnormalities. Understanding it helps you know what to watch for, and shows that you don't need to reach an “ideal” weight to protect your heart.

Two public health problems that overlap

Cardiovascular disease is the leading cause of death worldwide, with about 18 million deaths a year according to the World Health Organization (WHO), and the leading cause in the United States. In France, it is the second leading cause of death, with about 140,000 deaths a year.

Obesity is rising in parallel. It affects 18.1% of adults in France according to the OFÉO 2024 study, 40.3% in the United States according to the CDC, and 16% worldwide according to the WHO, or 890 million people. An analysis of 239 studies conducted across four continents, published in 2016 in The Lancet (Global BMI Mortality Collaboration), showed that each five-point increase in BMI above 25 was associated with about 30% higher mortality, mainly from cardiovascular causes.

A direct effect on the heart and blood vessels

Excess weight places extra work on the heart. It has to pump more blood, through a larger body mass and a more extensive network of blood vessels. Over time, the heart muscle thickens, and can then tire.

This extra burden explains the link with heart failure. In the American Framingham study, published in 2002 in the New England Journal of Medicine (Kenchaiah et al.), the risk of heart failure was about twice as high in people with obesity as in those with a normal body size.

Heart rhythm is affected too. Obesity promotes atrial fibrillation, the most common rhythm disorder, which raises the risk of stroke. The risk rises by about 30% for each additional five-point increase in BMI, according to a review published in 2015. Obesity also increases the risk of deep vein thrombosis and pulmonary embolism.

The central role of abdominal fat tissue

Not all body fat is equal for the heart. Visceral fat, located around the organs in the belly, is highly active: it releases fatty acids and inflammatory substances into the blood that damage artery walls and promote atherosclerosis, that is, plaque buildup. Fat located under the skin of the hips and thighs has a much smaller metabolic effect.

This is why waist circumference, which reflects abdominal fat, usefully complements BMI. The international INTERHEART study, conducted in 52 countries and published in The Lancet, showed that abdominal fat distribution predicted heart attack risk better than BMI itself. The usual reference points are a waist circumference of at least 94 cm in men and 80 cm in women, with risk markedly increased from 102 cm and 88 cm.

This also explains why a person of normal weight, but with a large waist circumference, can have increased cardiovascular risk. Conversely, some people with obesity have normal blood pressure, blood sugar, and cholesterol. This is sometimes called “metabolically healthy” obesity. Follow-up studies show, however, that this situation is often temporary and that cardiovascular risk remains somewhat higher than in people with a normal body size. It therefore justifies monitoring, without excessive worry.

A frequent association with other risk factors

Obesity very often comes with other cardiovascular risk factors.

• High blood pressure. Excess weight is one of its leading causes. Blood pressure falls by about one millimeter of mercury per kilogram lost. The Do I have high blood pressure? tool can help assess this.
• Type 2 diabetes, whose risk is multiplied by about seven with obesity. See the Am I at risk of diabetes? tool.
• Abnormal blood fats: high triglycerides and lowered “good” cholesterol (HDL).
• Sleep apnea, which raises blood pressure and promotes rhythm disorders. See the Do I have sleep apnea? tool.

These factors reinforce each other. A person's actual risk therefore depends on their combination, which is why an overall assessment matters more than looking at factors one by one. That's what the What's my cardiovascular risk? tool offers. BMI doesn't enter directly into the SCORE2 calculation, but its consequences on blood pressure and cholesterol are taken into account there.

A proven benefit, even with modest weight loss

You don't need to reach an “ideal” weight to see a benefit. A loss of 5 to 10% of initial body weight is enough to markedly improve blood pressure, blood fats, and insulin sensitivity. For someone weighing 100 kg (220 lb), that represents 5 to 10 kg (11 to 22 lb): a far more achievable goal than a radical transformation.

What do we know about the effect on cardiovascular events themselves? The answer is nuanced, and it has evolved in recent years.

Through lifestyle changes alone, the evidence is hard to establish. The American Look AHEAD trial, published in 2013 in the New England Journal of Medicine, followed more than 5,000 overweight people with diabetes for nearly ten years. The intensive diet and physical activity program improved weight, blood pressure, blood sugar, sleep, and quality of life, but did not significantly reduce the number of heart attacks and strokes. A further analysis, however, showed that participants who had lost at least 10% of their weight had about 20% fewer events.

With bariatric surgery, the benefit is established. The Swedish SOS study, published in 2012 in JAMA, showed about a one-third reduction in cardiovascular events in people who had surgery, compared with comparable people who did not.

With the newer medications, a milestone has been reached. The SELECT trial, published in 2023 in the New England Journal of Medicine, included 17,604 adults who were overweight or had obesity, without diabetes, who already had cardiovascular disease. Semaglutide reduced the risk of heart attack, stroke, or cardiovascular death by 20% over a little more than three years. These treatments, prescribed and monitored by a doctor, apply to only some people with obesity and add to, rather than replace, lifestyle measures.

Physical activity protects, whatever your weight

One point deserves emphasis: physical activity reduces cardiovascular risk even when weight doesn't change. People who are overweight but active and physically fit have a lower risk than people of normal weight who are sedentary. Moving regularly, without waiting to lose weight first, is therefore useful in its own right. The What's my activity/sedentary level? tool can help you find your starting point.

The other levers remain just as important. Quitting smoking, treating high blood pressure, or treating high cholesterol protects the heart independently of weight. Someone with obesity who doesn't smoke and whose blood pressure is well controlled has a much lower risk than is often assumed.

What to remember

BMI and waist circumference aren't just cosmetic indicators. They are markers linked to cardiovascular risk, with concrete levers for action: move more, lose a few kilograms, keep an eye on blood pressure, blood sugar, and cholesterol. The benefits are measurable from the first changes, without waiting for an ambitious weight goal, and your primary care doctor can help set priorities.

To calculate your own BMI and waist circumference, take the “Am I overweight or obese?” test.