Can coffee perk up your mood long term?

By Sophie Ramsey

BMJ Group News

What do we know already?

Coffee is the world’s leading source of caffeine, a stimulant known to boost alertness, as well as feelings of energy and well-being.

Although these caffeine perks are fleeting, researchers have wondered whether the stimulant might also have longer-lasting effects on mood. Some studies have suggested that people who drink more coffee are less likely to develop depression or commit suicide. But these studies have been fairly small or had other problems making them less reliable.

In the new study, researchers took data from a large, long-term trial tracking the diets, lifestyles, and health of thousands of US nurses. They identified more than 50,000 women who were free of symptoms of depression at the start of the study. They then followed them for 10 years, to see whether their caffeine consumption was related to their risk of later developing depression.

What does the new study say?

Women who consumed the most caffeine were 20 percent less likely to develop depression during the study than those who consumed the least.

When researchers looked only at coffee drinking, they found that women who drank two to three cups a day had a 15 percent lower risk of depression than those who drank less than one cup a day. And those who drank four or more cups had a 20 percent lower risk.

The researchers found no link between depression and decaffeinated coffee. They also found no connection with other sources of caffeine, including tea, soft drinks, and chocolate. However, it’s possible that not enough people consumed each of these as their primary source of caffeine (without also drinking coffee) to show a link.

How reliable is the research?

This study has a couple of advantages over earlier trials. First, it was very large, which means its findings are less likely to be down to chance. Second, it followed women who were initially free of depression for several years, to see if they eventually developed the condition. Other studies have looked at participants at only one point in time, to find out whether those with depression consumed more or less coffee than those without depression. This is a less reliable type of research, as it’s unclear which came first: depression or low coffee consumption.

However, the new study still can’t prove that drinking coffee - and not something else - lowered the women’s risk of depression. Depression is a complex illness and many factors can affect a person’s risk. The researchers took account of many of these, including how much the women exercised, their diet, their body mass index (BMI), whether they were active socially, and whether they had other health problems. Even so, the researchers might have missed something important.

What does this mean for me?

If you’re a woman and drink two or more cups of coffee a day, you may have a lower risk of depression than someone who drinks less. But it’s too soon to recommend drinking coffee as a way to prevent depression. Other studies will need to back up these findings, and explore whether there might be a benefit with other sources of caffeine and for men.

Also, it’s worth noting that caffeine can sometimes cause unpleasant side effects, such as sleeplessness, heart palpitations, and feelings of anxiety, particularly at higher doses.