Sugar is everywhere in the news, and most of the news isn’t good. Case in point: a new study suggesting that sugar may contribute to depression in men. The results add to a flood of findings linking sugar to a variety of both physical and mental health problems.
The study tracked the diets and medical conditions of 8,000 people over 22 years (all part of a larger study called the Whitehall Study II) using surveys about diet and doctors’ visits completed every few years. By keeping tabs on what the participants ate and the sorts of conditions they were seeing doctors to treat, the researchers could analyze correlations between diet and health outcomes. The one that popped out is that men who consumed 67 grams or more of sugar per day were 23% more likely to be diagnosed with depression in a five-year period than men who ate 40 grams or less.
None of the participants were being treated for mental illnesses at the start of the study. The connection between sugar and depression appeared relatively quickly during the first five-year survey, and remained more or less steady throughout the study. The researchers report that the effect was independent of the men's socioeconomic status, physical activity, drinking, smoking, other eating habits, body weight or physical health. The same correlation didn't appear for women in the study, though it's unclear why.
This isn’t the sort of study that can prove a cause-and-effect relationship, and self-reporting in surveys isn’t always reliable. But a 23% difference is significant even with those drawbacks. Saying sugar causes depression isn’t a reasonable conclusion from these results, but enough dots are connected to raise legitimate concern.
The researchers also looked for the reverse effect, that mood influenced the men to seek out sugary foods, but that connection didn't pan out. "We found no evidence for a potential reverse effect: participants did not change their sugar intake after suffering from mood disorders," said Anika Knüppel, PhD Candidate in Epidemiology and Public Health and the study's lead author.
For context, 67 grams of sugar a day is the rough equivalent of six donuts or about three average-size chocolate bars. It seems like a lot of sugar, about 25% higher than the daily recommendation. But the insidious thing about added sugar is how it turns up in foods we wouldn’t consider sugar-laden. Once you start counting up the sugar grams from foods throughout the day (bread, cereal and milk, for example), it’s not really that hard to reach 67 or more. And if you're a sugary beverage drinker, it won't take much at all--about two 12-ounce cans of your sugary soda of choice will get you there.
The finding is noteworthy because it lines up with what previous research has suggested: over-consumption of sugar triggers imbalances in certain brain chemicals, upping the chances of outcomes like depression and anxiety. In particular, it seems excess sugar impacts dopamine--the neurotransmitter that fuels the brain's reward system--not unlike a potent narcotic. Since addiction and mood disorders are closely associated, it may be that sugar plays a role similar to cocaine in powering the mood roller-coaster. And sugar is increasingly linked to cellular inflammation, which more evidence is revealing as a likely culprit in the onset of depression.
The bottom line is that there's a sturdy research basis for concern about excess sugar in our diets with respect to mental health, which adds to what we already know about sugar and physical health.
Which is not to say that any amount of sugar is damaging; our brains are dependent on sugar to function. Brain cells require two times the energy needed by all the other cells in the body, about 10% of our total daily energy requirements. That energy is derived from glucose (blood sugar), the brain's primary fuel. Sugar is not the brain's enemy--excess sugar is.
Do we have conclusive proof that over-consumption of sugar causes depression? No. Do we have a decent indication that excess sugar is at least a contributing factor to depression in a percentage of the population? Yes. More research is needed to explore what's going on, but at present we have more than enough evidence about sugar's overall impact on health to be vigilant about how much we're consuming.
The latest study was published in the journal Scientific Reports.