A new study has produced a surprising result about cannabis and the heart.
People who regularly used cannabis had about 9% fewer premature heartbeats on days when they smoked or vaped cannabis than on days when they did not use it.
The finding does not mean cannabis is good for the heart.
Researchers at the University of California, San Francisco stressed that the study looked only at short-term effects in regular users and cannot answer whether long-term cannabis use raises or lowers the risk of heart disease.
The research was published in the Journal of the American College of Cardiology. It was led by UCSF researchers including Dr. Gregory Marcus, a professor who studies abnormal heart rhythms.
Cannabis use has become increasingly common as more places legalize it for medical or recreational purposes. At the same time, doctors are trying to understand how the drug affects the heart, blood vessels and other parts of the body.
Previous studies have linked cannabis use with several cardiovascular concerns. However, many of those studies were observational, meaning researchers compared people who chose to use cannabis with those who did not.
That type of research is useful but has an important weakness. Cannabis users and nonusers can differ in age, diet, tobacco use, alcohol use, exercise and many other factors that can make it difficult to determine whether cannabis itself caused an observed health difference.
The UCSF team used a different approach. They recruited 108 adults who regularly smoked or vaped cannabis but had never been diagnosed with a heart rhythm disorder.
For 14 days, each participant was randomly assigned each day either to inhale cannabis or to avoid it. This allowed the same person to be compared on cannabis-use days and cannabis-free days.
Participants continued living their normal lives rather than staying in a laboratory. Throughout the study, they wore devices that continuously recorded their heart rhythm, physical activity and sleep, while another monitor tracked blood glucose.
The heart monitor gave researchers a detailed record of every heartbeat. They were particularly interested in premature beats, which are extra or early electrical signals that briefly interrupt the heart’s usual rhythm.
Some of these early beats begin in the heart’s upper chambers and are called premature atrial contractions, or PACs. Others begin in the lower pumping chambers and are called premature ventricular contractions, or PVCs.
Occasional premature beats are common and many people never notice them. However, frequent PACs are associated with a greater future risk of atrial fibrillation, a common abnormal rhythm that can increase the risk of stroke.
Frequent PVCs can also be important because high numbers have been associated with heart problems, including heart failure in some people. Researchers therefore want to understand what causes the frequency of these extra beats to rise or fall.
The study found that cannabis use was associated with fewer premature heartbeats overall. The difference was mainly explained by a reduction in PACs, while the researchers did not find a significant change in PVCs.
This result was the opposite of what the investigators had expected. Marcus said the surprise illustrates why randomized studies are valuable, because carefully collected data can challenge assumptions formed from earlier research.
The team also expected cannabis use might affect movement, sleep or blood sugar. Yet they found no significant differences in daily step counts, sleep duration or glucose levels between cannabis and abstinence days.
The findings should be interpreted cautiously. The study included people who already used cannabis regularly, so their bodies may respond differently from those of people who rarely use cannabis or have never used it.
The trial also lasted only two weeks and measured immediate effects. It cannot tell researchers whether smoking or vaping cannabis for months or years changes the risk of atrial fibrillation, heart attack, stroke or other cardiovascular diseases.
Inhaled cannabis may also expose the lungs and cardiovascular system to substances that have effects not captured by counting premature heartbeats. A small reduction in PACs does not establish that the overall health effects of cannabis are positive.
The most interesting part of the research may therefore be the biological clue it provides. If scientists can discover why cannabis temporarily reduced PACs, they may learn more about the mechanisms that trigger these early heartbeats and eventually identify safer ways to control them.
For now, the study should not be used as a reason to start cannabis or change medical treatment. Its main contribution is showing that cannabis and cardiovascular health have a more complicated relationship than simple assumptions may suggest, and that longer randomized studies are needed.
If you care about heart disease, please read studies that herbal supplements could harm your heart rhythm, and how eating eggs can help reduce heart disease risk.
For more health information, please see recent studies that apple juice could benefit your heart health, and results showing yogurt may help lower the death risks in heart disease.
Source: University of California, San Francisco
