“Life, liberty, and the pursuit of happiness.” This well-known phrase appears in the United States’ Declaration of Independence, and hints at the importance of happiness to our health, but how important is it? An international team of researchers studied the effects of happiness on longevity, and why unhappy people tend to have life-threatening poor health. Their findings, published in The Lancet, suggest it’s not happiness that leads to a longer life, but other factors instead.

For years, researchers have mistakenly equated being unhappy with a shorter lifespan. This isn’t necessarily the case. Instead, it’s the behaviors that come with unhappiness, according to the study. For example, smokers tend to be unhappier than non-smokers, and because smoking is associated with increased risk of death, past studies have forcibly linked unhappiness to death.

In order to disentangle the link between unhappiness and death, researchers analyzed data on over a million UK women aged 55 to 63 for 10 years. During this time, they were asked to rate their own health, happiness, stress, feelings of control, and whether or not they felt relaxed. Researchers also tracked the women’s hospital admissions and deaths through electronic records, and found 31,531 had died by the end of the study.

Results showed that those who reported being “happy most of the time” (39 percent) were in good health, while those who said they were “usually happy” (44 percent) were in better health when compared to those who reported being unhappy — these people, who comprised 17 percent of the cohort, tended to be in poor health from the beginning of the study. It was only after they became sick that they reported lower rates of happiness, the study found. This was supported by a “substantial minority” of healthy women who reported being stressed or unhappy but were no more likely to die than those who were generally happy. So, it turns out poor health causes unhappiness, not the other way around.

“Illness makes you unhappy, but unhappiness itself doesn't make you ill,” said the study’s lead author Dr. Bette Liu, a researcher at the University of New South Wales, Australia, in a press release. “We found no direct effect of unhappiness or stress on mortality, even in a 10-year study of a million women. ”

While happiness may have a lesser effect on our lifespan than we’ve come to believe, it doesn’t mean being unhappy is harmless. It could be a subtle side effect of an illness, such as those observed in the study — high blood pressure, diabetes, asthma, arthritis, depression, and anxiety. Furthermore, it could also be a catalyst for self-harm, increasing a person’s risk of alcohol abuse, suicide, or other harmful behaviors, thus giving us a reason to get checked up, be in good health, and find the joy in life.

Source: Liu B, Floud S, Pirie K, Green J, Peto R, and Beral V. Does happiness itself directly affect mortality? The Lancet. 2015.