Numerous studies have examined how COVID-19 might lead to more cases of high blood pressure—but most don’t include enough people from historically marginalized groups.

Jeremy Goldhaber-Fiebert, PhD, has conducted extensive research within the California Department of Corrections and Rehabilitation since the COVID-19 pandemic hit, so he turned to the residents of the state’s prisons to dig deeper.

“Although the vast majority of COVID-19 cases globally have not been fatal, many have involved acute symptomatic disease, hospitalizations, and ongoing comorbidity,” writes Goldhaber-Fiebert, a decision scientist and professor of health policy. “Understanding of the long-term health effects of COVID-19 is growing, but remains incomplete.”

Goldhaber-Fiebert and his colleagues examined nearly 40,000 incarcerated residents in the country’s second-largest prison system—and followed them for more than four years. The study published in the American Journal of Epidemiology provides one of the most detailed analyses to date of the long-term effects of COVID-19.

The other authors of the study are David Studdert, LLB, ScD, MPH, a professor of health policy and of law; Shannon Phillips, an epidemiologist and data analyst at Stanford Health Policy; Kimberly Lucas, MPH, an epidemiologist with the California Correctional Health Care Services, and Donna Jacobsen, DO, who is also with the California Correctional Health Care Services.

They found COVID-19 is associated with significant increases in incident hypertension in the large, racially and ethnically diverse prison population. And the elevated rates of hypertension incidence endured as long as two years after infection.

“Our findings join a growing evidence base linking COVID-19 and hypertension, and provide valuable information to decision-makers in both carceral and non-carceral health care and public health settings who are considering whether to increase screening among people who have had COVID-19, particularly among those who have other risk factors for hypertension.”

The Cohort

The research team said earlier studies have suggested COVID-19 may raise the risk of developing high blood pressure, but included too few people from historically marginalized people—especially Hispanic and Black individuals—despite their higher rates of both COVID-19 and hypertension. Other studies rely on small samples, making results less reliable, or they fail to fully account for pre-existing high blood pressure, medications, or other conditions that affect blood pressure. Others lack consistent testing or careful follow-up, which can bias results and make it harder to know whether COVID-19 itself is driving up the increase in hypertension.

The Stanford Health Policy-led team examined 39,746 people who were in 31 California state prisons from January 2019 until March 2020, right as the pandemic hit the United States. The individuals had no pre-pandemic diagnosis of high blood pressure and were not taking any medications for it. The researchers used measures of body weight and blood pressure taken by the healthcare system both before and during the pandemic as well as results from the frequent and systematic testing for COVID-19.

The researchers followed the data on these individuals until March 2023. They found that of all the participants, 21,480 tested positive for COVID-19 prior to any high blood pressure diagnosis. The rate of new high blood pressure cases among those who had COVID-19 was 32.5 cases per 1,000 person-years—compared to 27.1 for those who didn’t have COVID.

After adjusting for baseline characteristics—such as age, gender, race and ethnicity and medical history—and accounting for potential confounders, they found that the risk of developing hypertension after a COVID-19 infection was still significantly higher than normal. This was particularly the case in people with higher baseline body weight, older age, and higher blood pressure before the pandemic.

The authors note that while the study focuses on prison residents—whose risks differ from those in the general public—the same underlying biology likely applies to everyone. What they learned about COVID-related high blood pressure in prisons can help explain patterns in the wider population.

“Our findings have implications for justice health policy. Carceral systems, hospitals and clinics, and clinicians that provide care to incarcerated individuals should be award that COVID-19 elevates residents’ risk of developing new-onset HTN, in both the short and long term,” they write. “This knowledge can shape approaches to preventive care and disease surveillance. It should also motivate and guide efforts to link residents to appropriate health insurance and health care services upon their release.”