More Trees Means Less CVD, Florida Census Data Suggest

People who live in areas with more vegetation—or greenness—have consistently lower odds of developing cardiovascular disease even after controlling for a wide array of population variables, according to new US Census-based data from Florida.

“We're looking at greenness as a potentially modifiable factor that may be able to move the needle of public health,” lead author Scott C. Brown, PhD (University of Miami Miller School of Medicine, FL), told TCTMD. “Obviously there's a cost associated with planting trees, but it may be ultimately a preventive intervention that may cost [less] than the cost of medical care for chronic diseases if we can prevent the diseases in the first place.”

Their results were published online last month in the Journal of the American Heart Association.

For the study, Brown and colleagues analyzed data from 229,034 US Medicare beneficiaries in Miami-Dade County, FL, to determine the effect of consistently high or low “precision greenness” on the 5-year incidence of new acute MI, atrial fibrillation, heart failure, ischemic heart disease, stroke/transient ischemic attack, and hypertension. The metric describes vegetation at the census-block level.

The researchers split regions into tertiles of greenness between 2011 and 2016 according to Normalized Difference Vegetation Index values, and they adjusted for individual age, sex, race, ethnicity, baseline cardiovascular disease conditions, neighborhood income, and walkability. Those living in the highest compared with the lowest tertile of greenness were generally younger (mean age 73.8 vs 74.7 years), were more likely to be male (43.4% vs 40.7%), had a higher neighborhood median household income ($82,100 vs $40,200), were less likely to be Hispanic (42.1% vs 82.5%), and had a lower average Walk Score, a measure of walkability.

Compared with people living in the lowest greenness tertile, those in the highest tertile were less likely to develop any new cardiovascular conditions (OR 0.91; 95% CI 0.84-0.99). Notably, among those with any new cardiovascular conditions, there did not seem to be an association between greenness and the total number of new cardiovascular conditions.

“It's pretty remarkable to show [the impact of greenness] over that small period of time, suggesting that over even longer periods of time, we might even show even stronger effects of greenness on CVD incidence,” Brown said.

Over even longer periods of time, we might even show even stronger effects of greenness on CVD incidence. Scott C. Brown

As for what might be at play, he acknowledged the findings are only hypothesis generating at this point. It’s possible that greenness could be related to pollution, for which high levels have been associated with CVD risk in several studies. Also, greenness can combat heat island effects, which are especially prevalent in Florida, and it can also affect stress levels and physical activity, Brown said. “There's a lot of future work that needs to be done to tease out these mechanisms.”

Commenting on the study for TCTMD, Aruni Bhatnagar, PhD (University of Louisville, KY), said in an email: “This is an important study that adds to a growing body of literature suggesting that living in areas of high surrounding greenness decreases the risk of cardiovascular disease. The extent of risk reduction associated with the level of greenness is also consistent with prior estimates.”

What makes this study special is that it delves into the census-block level, he continued. “The data obtained from large-scale studies over several zip codes or even entire cities and countries are not actionable,” Bhatnagar explained, adding that it remains unknown “on what scale greenness exerts its influence.”

Being able to identify which blocks have less vegetation can lead to specific improvement efforts to increase public health, he concluded.