Sweden, Denmark and the United Kingdom are at the top of this blood-pressure-based happiness group, while Germany, Portugal and Finland are at the bottom, according to Andrew Oswald of the University of Warwick in England and David Blanchflower of Dartmouth College in New Hampshire.

The researchers say that doctors have known for a long time that blood pressure is one measure of an individual's health, but this is the first to demonstrate a connection between nations' happiness and blood-pressure levels.

The researchers believe that the blood-pressure rankings could offer a way for policymakers to move away from simply focusing on maximizing a country's gross domestic product.

The researchers also found that mental health in each country is inversely correlated with its rate of hypertension, according to the study published by the National Bureau of Economic Research in Massachusetts.