Chickenpox is caused by the varicella-zoster virus, and once a person has been exposed to this virus, it can remain within the body in a dormant state.
In some cases, many years later, the virus can reactivate and cause illness, which is referred to as shingles, or herpes zoster. To date, scientists are not entirely sure why the varicella-zoster virus becomes active again.
Symptoms of shingles include a painful rash involving blister-like sores. The rash normally forms in a band or small area on one side of the body or face, and it can last up to 14 days. The pain associated with shingles can be substantial, and, in some cases, it can continue for years after the rash has gone. This is a condition called post-herpetic neuralgia.
In the United States, an estimated 1 in 3 people will develop shingles at some point during their lifetime. The risk of shingles increases with age, occurring most commonly after the age of 60. In all, there are around 1 million cases of shingles each year in the U.S.
Shingles and cardiovascular risk
In recent years, some studies have hinted at a relationship between shingles and an increased risk of stroke and heart attack. For instance, a study published in the journal PLOS Medicine in 2015 concluded, "Stroke and MI [myocardial infarction] rates are transiently increased after exposure to herpes zoster."
Recently, researchers from South Korea set out to examine this link in one of the largest studies of its kind. The team delved into the National Health Insurance Service's "medical checkup" database. They collated information regarding the incidence of newly diagnosed shingles, stroke, and heart attack.
The study was headed up by Sung-Han Kim, Ph.D., from the Department of Infectious Diseases at Asan Medical Center in Seoul, South Korea. The results are published this week in the Journal of the American College of Cardiology.
They followed almost 520,000 patients from 2003 to 2013. Within this timeframe, there were 23,233 shingles cases. These cases were then matched to 23,213 people who did not develop shingles, or controls.
The shingles group were found to share certain traits - for instance, they were more likely to be female, older, have higher blood pressure and high cholesterol, and have diabetes. These are all common risk factors for heart attack and stroke.
Additionally, the shingles group had a lower alcohol intake than average, were less likely to smoke, exercised more frequently, and were in a higher socioeconomic class.
Heart attack risk increased by 59 percent
Once the analysis had been completed, the risk of cardiovascular events was shown to be elevated in the shingles group. The combined risk of heart attack and stroke was 41 percent higher. When cardiovascular risks were broken down and calculated separately, stroke and heart attack risk increased by 35 percent and 59 percent, respectively.
This increased risk was highest for people under the age of 40. Interestingly, because of their younger age, these individuals had fewer risk factors for atherosclerosis.
Cardiovascular risk was highest in the first 12 months following the shingles diagnosis, and it slowly decreased over time. In the control sample, the risks were evenly distributed.
"While these findings require further study into the mechanism that causes shingles patients to have an increased risk of heart attack and stroke, it is important that physicians treating these patients make them aware of their increased risk."
Sung-Han Kim, Ph.D.
The link between zoster reactivation and cardiovascular events has now been strengthened, but the exact reasons behind this relationship may take longer to unravel.