The study involved more than 260,000 Americans ages 50 and
up. All had originally taken part in a survey in which they recorded their
daily soda, tea, fruit punch, and coffee consumption. A decade later,
researchers checked in again and asked whether they had been diagnosed with
depression in the intervening years.
People who drank more than four cans or cups of soda per day
were 30 percent more likely to have developed depression, compared to those who drank
no soda. Further analyses showed that the association was stronger for diet
soda than for regular soda.
The depression risk was also higher for diet fruit punch and
diet iced tea, compared to regular versions of those beverages. Interestingly,
coffee seemed to have the opposite effect: People who drank four or more cups
of coffee per day were about 10 percent less likely to have developed depression than
those who drank no coffee.
What’s the connection between diet drinks and depression?
Unfortunately, there’s no clear answer to that question yet. So far, only a
summary of the study has been released. Lead author Honglei Chen, MD, PhD, and
his colleagues will present more details about their findings at the annual
meeting of the American Academy of Neurology in March.
Even then, however, definitive answers will await further
research. Although this type of study can find intriguing associations, it’s
not designed to sort out cause and effect. For now, scientists can only
speculate about possible explanations.
One possibility is that aspartame—an artificial sweetener
used in many diet drinks—might affect the brain in ways that increase the risk
for depression. One recent
study showed that giving mice aspartame caused oxidative stress in their
brains. It also inhibited three important brain chemicals: serotonin,
noradrenaline, and dopamine. In humans, depression may be related to low levels
or diminished activity of these chemicals.
Suspect No. 2:
Obesity and Diabetes
Another possibility is that diet drinks and depression are
linked indirectly through a third thing they have in common: obesity and
diabetes. Both conditions are common in older adults. And people who are trying
to lose weight or keep their diabetes under control are particularly likely to
reach for a diet drink instead of one sweetened with sugar. Being obese or having
diabetes also increases the chance of becoming depressed. So it could be
that the higher depression risk seen in diet soda drinkers was nothing more
than guilt by association.
A lot remains to be learned. In a statement about the new study,
Dr. Chen summed up what’s known so far: “Our research suggests that cutting out
or down on sweetened diet drinks or replacing them with unsweetened coffee may
naturally help lower your depression risk. More research is needed to confirm
these findings, and people with depression should continue to take depression
medications prescribed by their doctors.”