Each person had asthma or at least one allergic disorder, such as a respiratory, food, or skin allergy.
In addition to the risk for high blood pressure, the research also found a higher risk for coronary heart disease for people between the ages of 39 and 57 with allergies. Coronary heart disease occurs when plaque builds up in the walls of the arteries that supply blood to the heart.
Based on their findings, researcher encouraged clinicians to add a cardiovascular risk assessment to clinical examinations of people with asthma and allergies.
"For patients with allergic disorders, routine evaluation of blood pressure and routine examination for coronary heart disease should be given by clinicians to ensure early treatments are given to those with hypertension or coronary heart disease," said lead study author Yang Guo, a postdoctoral researcher at Peking University Shenzhen Hospital in China, in a statement.
'Question Is Why'
While prior research has shown a connection between having allergies and an increased risk of cardiovascular disease, "the question is why?" said pulmonologist Dr. Raj Dasgupta, an assistant professor of clinical medicine at the Keck School of Medicine at the University of Southern California.
"We can't really show causality, but science does show it's connected to pro-inflammatory mediators, things that trigger inflammation in the body," said Dasputa, who was not involved in the study.
Histamines, for example, boost blood flow into the area the allergen attacks, which causes the immune system to send antibodies, thus triggering inflammation. That's why many allergy medications are antihistamines, designed to counter that inflammatory response.
Although inflammation is the body's way of fighting pathogens, an overactive or long-lasting response is an underlying factor in many chronic diseases, including diabetes, high blood pressure, and heart disease.
Antihistamines constrict blood flow, as can other over-the-counter allergy medications such as those that contain the "letter D, which is pseudoephedrine," Dasgupta said. "Those narrow the blood vessels not only in the nose but the rest of the body, which can lead to high blood pressure and an increased heart rate."
Other medications can also have a negative effect on the cardiovascular system, including steroids often prescribed for asthma attacks and emergencies, Dasgupta said.
"Steroids increase blood pressure, they increase blood sugar and both high blood pressure and high blood sugar levels are very important risk factors for coronary artery disease and stroke," he said. "They can also cause weight gain, which is another risk factor."
Add all of this to other triggers of chronic inflammation in the body -- such as sugar, highly processed and fried foods, stress, poor sleep, a lack of exercise, and pollution, to name a few -- the answer "could be multifactorial -- the immune response, medications and all these things put together," Dasgupta said.