The human environmental studies would include things such as the population in a country, how a country's economy is doing, and more.
The study began in 1988 and included patients 17 to 80 years old.
The four studies included a total of about 2,000 patients.
The study included more than 27,000 people in 52 countries.
The study included 1,653 men over the age of 50.
The study included 13,882 women and 13,618 men in 29 countries.
The study included nearly 30,000 men and women without known heart disease.
The study also included a look at crime in the area.
The new study included 740 men from six studies; their average age was about 55.
The study included more than 3,000 adults in their 70s.