ADHD and addiction are rarely thought of as positive conditions. Most of the time, they aren't. However, a gene linked to the pair may be responsible for helping people to live to the age of 100 and longer.

A study recently published in the Journal of Neuroscience examined the role that the gene DRD4 may play in longevity. The genotype, which is responsible for coding a receptor of the brain chemical dopamine, has been found to be 66 percent more common in people who live to the age of 90 or older. The gene means that the response to the dopamine system, prompting feelings of pleasure and reward, is lower.

If not well monitored, the gene can lead to an all-encompassing pursuit of good feelings, prompting addiction and the dysfunctional behavior so common in individuals with ADHD, according to the TIME. That is why this study may seem counterintuitive; after all, ADHD has been linked to an increase in early deaths prompted by risk-taking behaviors, like promiscuity and infidelity. The behaviors undertaken by people with ADHD can cause an increased risk of contracting sexually transmitted diseases and have been linked to a 50 percent increase in car accidents.

However, the study suggests that if people with the gene make it through the risky years of adolescence and young adulthood, it can have positive benefits. For example, a common trait in ADHD is an inability to sit still. That can prompt individuals to avoid a sedentary lifestyle - and the common diseases associated with it. The gene variant increased longevity mostly in women, not altogether surprising since risky behaviors and addiction are more often seen in young men.

The study was conducted among 1,000 seniors aged 90 to 109 years old who lived in the Leisure World retirement community in Laguna Woods, California. The group was part of a 14,000-person collection of highly educated people who had first been studied in 1981. Most were of European ancestry.

The researchers found that the gene was more common in the oldest participants, and the gene carriers were also more physically active than their peers who lacked it. Researchers suspect that they are more likely to seek arousal and, as a result, are more likely to perform physical activity. This finding was true in 1981 as well as today.

A second experiment modified some rats to lack the dopamine variant. The modified mice lived 7 to 10 percent shorter lives than their peers, in part because they moved much less. Companionship and an enrichment environment that provides a lot of opportunity for learning also did not help the knockout rats, though it did help their peers live longer. The study reinforces the interplay found between genes and environment.