Three Most Dangerous Underlying Conditions for COVID-19

High-risk condition: Obesity

What the numbers say: Obese people diagnosed with COVID-19 are more than twice as likely to be hospitalized and about 50 percent more likely to die compared to patients who are a healthy weight, according to a meta-analysis published in Obesity Reviews. (Obesity is defined as those with a body mass index, or BMI, of 30 or above.)

While obesity is often linked to other health problems, doctors say they have been struck by how hard COVID-19 hits even those obese patients who have no other underlying conditions.

"I think the one [health condition] that has really stuck out is obesity,” said Jakob McSparron, M.D., a critical care doctor at Michigan Medicine in Ann Arbor, Mich. “In particular, it seems as though obesity among younger patients is a notable risk factor."

Why it's dangerous with COVID-19: Obesity can make it harder for a person's lungs to expand, impairing breathing and oxygenation. In addition, extra fat, especially around the belly, is linked to chronic inflammation that can weaken the immune response. Obesity is also believed to increase your risk of blood clots.

What you can do: Because your risk of complications from COVID-19 is directly correlated to your BMI, if you're among the 42 percent of Americans who are obese, even a small amount of weight loss can make a difference, said cardiologist Dariush Mozaffarian, M.D., dean of Tufts Friedman School of Nutrition Science and Policy.

"It takes weeks, not years,” he said. “It's very well documented that even losing five pounds makes a difference in your metabolic health. With a few small lifestyle changes — eat a little healthier, exercise a little more, get more sleep — you could very plausibly lower your risk of severe illness from COVID-19."

High-risk condition: High blood pressure

What the numbers say: When researchers analyzed 22 studies from eight countries last year, they found that high blood pressure was present in 42 percent of hospitalized COVID-19 patients, making it the most prevalent health condition by far. Even more stunning: Those patients had twice the risk of death compared with patients without high blood pressure, said Vikramaditya Samala Venkata, M.D., one of the study's authors and a hospital medicine physician at Cheshire Medical Center in Keene, N.H.

The news isn't all bad, however. The Clinical Infectious Diseases study on COVID-19 mortality found that hypertension on its own raised the death rate only for those under age 40, said study author Anthony Harris, M.D., an epidemiologist at the University of Maryland.

For those age 40 and older, mortality risk increased only if their high blood pressure had caused a complication such as heart damage or chronic kidney disease.

Why it's dangerous with COVID-19: Experts believe COVID-19 damages the cells that line blood vessels, causing clots and making it harder for them to carry oxygen.

What you can do: Follow your doctor's advice to keep your blood pressure under control. Studies show patients with unregulated high blood pressure are at greater risk from COVID-19 compared with patients who take medication to control it.

High-risk condition: Diabetes

What the numbers say: An analysis of the medical records of 61 million people in England published in The Lancet Diabetes & Endocrinology found that the risk of dying from COVID-19 was almost three times higher for people with type 1 diabetes and almost twice as high for people with type 2 diabetes, compared with those without.

Again, Harris's Clinical Infectious Diseases mortality study found that whether the diabetes had caused a complication such as organ damage or kidney disease played a role.

"For most ages, if you have just plain old diabetes with no complications, [or] plain old hypertension with no complications, you either had very little risk or no higher risk” of death, Harris said.

Why it's dangerous with COVID-19: High blood sugar weakens the immune systems, making it harder for your body to fight off infections. “Diabetes puts you at risk for both cardiovascular complications and infectious complications — and we know both of those things are common with COVID,” said Luke Davis, M.D., a critical care physician associated with the Yale School of Public Health.

What you can do: Stay on top of your blood sugar levels. Patients with well-controlled diabetes have a COVID-19 death rate of about 1 percent, according to a study published in Cell Metabolism. In those with poorly controlled disease, however, the rate rises to 11 percent.

Rachel Nania also contributed to the reporting of this story.