Long COVID linked to 14% higher risk of new high blood pressure in Stockholm adults

People with long COVID tend to spend a lot of time in clinics, and every visit is a chance for someone to wrap a cuff around their arm. That makes new research from Stockholm both interesting and tricky to read. Among more than a million working-age adults, those diagnosed with long COVID were more often diagnosed with high blood pressure over the next few years. The question the result leaves is how much of that reflects higher blood pressure and how much reflects more measuring.

The paper, published on October 10 in the Journal of the American Heart Association, followed 1,221,570 adults aged 18 to 65 in the Stockholm region. In the main analysis, long COVID was associated with a rate of new hypertension diagnoses about 14% higher than in people without long COVID, and the link was almost the same in women and men. The researchers, led by Pia Lindberg and Axel Carlsson, had already reported more heart disease after long COVID in the same records. This paper turns to blood pressure, among people who were never sick enough with COVID-19 to be admitted to hospital.

What long COVID is, and how the Stockholm registry captured it

Long COVID has no single test. A World Health Organization working group defined it in 2021 as symptoms that usually start about 3 months from the onset of COVID-19 and last at least 2 months and cannot be explained by an alternative diagnosis. Common symptoms include fatigue, shortness of breath, and cognitive dysfunction, meaning problems with memory and concentration. It has been listed in the ICD-10 classification as post-COVID-19 condition since September 2020, the month the World Health Organization created its diagnosis code, U09.9.

That code is how this study identified long COVID. The researchers used MIRACLE-S, a research database built from the Stockholm region’s health records, which covers all providers of healthcare for around 2.5 million residents of Stockholm County. In the team’s earlier paper on heart disease, which used the same records, about 90% of adults were registered with a primary care provider, so most of the region’s working-age population passes through the data.

The hypertension study took in adults aged 18 to 65 years without prior hypertension and without a hospital stay for acute COVID-19, and followed them from October 2020 to January 2025. Of the 1.2 million, 8,365 (0.7%) received a long COVID diagnosis: 5,578 women and 2,787 men. Everyone else in the cohort, without the diagnosis, formed the comparison group. In the team’s earlier paper on the same registry, that group took in everyone without a long COVID diagnosis, regardless of whether they had a recorded acute COVID-19 diagnosis, so people who had COVID-19 and recovered sat alongside people who never had it. The outcome was a new diagnosis of hypertension in the medical record.

The 0.7% is a share of all adults in the region, infected or not. Estimates cited in the team’s earlier work put long COVID at 10% to 30% of individuals who have had an acute infection, so the people with the code are likely the minority whose symptoms reached a doctor and a diagnosis.

How much more often hypertension was diagnosed

By the end of follow-up, 16% of women and 24% of men with long COVID had been diagnosed with high blood pressure. Those are totals; the extra risk is the 14% figure below. The long COVID group showed an early and consistently higher rate of diagnoses than everyone else, pulling ahead soon after the long COVID diagnosis and staying ahead.

In the main analysis, which compares rates over time, long COVID went with a 14% higher rate of new hypertension diagnoses. The figure was 13% in women and 15% in men. Women and men were analyzed separately. Two in three people with the diagnosis were women, and the absolute rates differ a lot between the sexes, as the 16% and 24% show, yet the relative increase was almost the same. The researchers adjusted for age, socioeconomic status, comorbidities, mental health and how often each person had used healthcare before the pandemic, and the estimate barely moved as each layer was added.

A 14% higher rate is modest. For comparison, the same team’s heart disease paper found that long COVID went with roughly double the rate of a combined set of heart problems in women and a third more in men. Heart rhythm problems rose most. High blood pressure is common to begin with: the number of people worldwide living with it has doubled since 1990, to about 1.28 billion adults aged 30 to 79, according to a large international analysis. A small relative rise in something that common still adds up to many people, but it is not a large effect for any one person.

More doctor visits, more blood pressure checks?

The main alternative explanation is what epidemiologists call detection bias. Someone with long COVID may see a doctor many times a year for fatigue or breathlessness, and each visit can include a blood pressure reading. A person without long COVID, whose blood pressure crept up by the same amount, might go years without being checked. A difference in diagnoses can then appear without any difference in blood pressure.

The Stockholm team was alert to this. Writing about heart disease in the same records, they acknowledged that people with long COVID “may also have had more frequent healthcare contacts, potentially increasing the likelihood of detecting cardiovascular disease”. In the hypertension study they adjusted for healthcare use before the pandemic, and the link held. That helps, but it cannot fully remove the extra checking that comes after a long COVID diagnosis, which is the period that matters here.

A study from California offers an independent check. Researchers followed 39,746 people held in 31 California state prisons through the pandemic, all of whom had blood pressure and weight measured both before and during it. COVID-19 infection went with a 44% higher rate of new hypertension, and the authors concluded that potential confounding from extra blood pressure testing after infection cannot explain these results. The prison work looked at infection, not long COVID, but it suggests the link between COVID-19 and blood pressure is not simply an artifact of who gets measured.

Why long COVID might raise blood pressure

The new paper opens by noting that long COVID has been linked to persistent autonomic and vascular abnormalities. The autonomic nervous system is the automatic control system that sets heart rate and the tightness of blood vessels, and the vascular system is the blood vessels themselves. Both help set blood pressure.

In the heart disease paper, the authors list persistent endothelial dysfunction, autonomic dysregulation, and immune-mediated injury among the proposed drivers of heart problems after COVID-19. Endothelial dysfunction means the inner lining of the blood vessels stops working properly. They also point to reports of more frequent postural orthostatic tachycardia syndrome in people with long COVID, a condition in which the heart races on standing up. In the hypertension paper, the authors suggest that infection may contribute to vascular and autonomic dysregulation affecting blood pressure. None of these routes was measured in the registry, so they remain explanations to test.

Earlier studies of COVID-19 and new hypertension

The finding fits a pattern from other countries, though most earlier studies asked about infection in general, not long COVID. In a New York health system, 10.85% of nonhospitalized patients with COVID-19 had new persistent hypertension six months later. That was about one and a half times the rate seen after influenza, a comparison that helps separate COVID-19 from the effects of any respiratory infection.

In a large study of US veterans published in 2022, cardiovascular risks after infection were evident even among individuals who were not hospitalized during the acute illness, and they rose with the severity of the initial infection. The Stockholm results extend that picture to blood pressure in a working-age population with a formal long COVID diagnosis, in a country where nearly everyone is in the same public health system.

Gaps in the long COVID hypertension study

The Stockholm analysis counts diagnoses, not blood pressure readings. It cannot say how high anyone’s blood pressure was, whether it was treated, or whether it came down again as long COVID symptoms eased.

Long COVID itself was defined by a code, and codes miss people. The code came into clinical use in these records in October 2020 and took time to catch on, so early cases were probably undercounted. The team has also noted that women may be more likely than men to seek healthcare for lingering symptoms, and so to receive the diagnosis. The registry does not capture certain lifestyle factors such as exercise and diet, nor vaccination status or repeat infections.

Because the records come from routine care, the population is enriched for individuals with healthcare contact and carries more existing illness than the general population. That can push absolute rates such as the 16% and 24% above what a community survey would find. Relative comparisons are less affected. Vaccination is unlikely to explain much either way, the team argued, since coverage among Stockholm adults was about 80% or higher for most of the period.

Everyone studied was aged 18 to 65 and lived in a high-income region with universal healthcare, so the results may not carry over to older people or to places where access to doctors differs.

What the results mean for people with long COVID

The authors conclude that their results support “structured monitoring and risk management in individuals with persistent post-COVID symptoms”. Their analysis tested no monitoring program or treatment. How blood pressure is checked and managed for a person with long COVID is assessed by their doctor.

The Stockholm records show a small, consistent rise in high blood pressure diagnoses after long COVID, and leave open how much of it more frequent checking explains.