When we're tucking into a sugary treat, the last thing on our mind is what the impact may be on our mental health. Mounting evidence suggests there is a link between high sugar intake and our long-term mental health, and perhaps that afternoon pick-me-up may be doing more harm than good.
A recent study published in the journal Scientific Reports identified a greater risk of depression in men who consumed large amounts of sugar in their diet.
It can be argued that feeling depressed may lead to increased sugar consumption, rather than the other way around. However, researchers used data from the Whitehall II study - a large group of civil servants in the U.K. - which showed that sugar consumption came before depression, rather than being a consequence of it.
So while there are an increasing number of studies looking at the implications of diet on mental health, it is difficult to study the exact causes and mechanisms that link the two.
What is the evidence? And how can sugar, such a simple molecule, wreak such havoc in our brains?
In 2002, a study of overall sugar consumption per person in six different countries (Canada, France, Germany, Korea, New Zealand, and the United States) - published by Dr. Arthur Westover, from the University of Texas Southwestern Medical Center in Dallas - implicated sugar as a factor in higher rates of major depression.
Since then, several other research teams have investigated the effect of diet on mental health. For example, consumption of processed and fast food - including hamburgers, pizza, and fried foods - was found to be higher in both youngsters and adults with increased rates of depression.
Likewise, female U.S. seniors with high levels of sugar in their diet had greater rates of depression than those who consumed less sugar.
Sugar-sweetened beverages, especially soft drinks, have increased in popularity and are now consumed around the world. But a study of Chinese adults - who traditionally drink unsweetened tea - showed that those who drank soft drinks had higher rates of depression.
While these studies did not set out to find the biological mechanism by which sugar affects mental health, they add to the body of evidence reporting on the link between the two.
In further research, a study by researchers from the Department of Neurobiology at Huazhong University of Science and Technology in Wuhan, China, performed on diabetic rats showed that high blood glucose, a simple sugar, led to inflammation and neuronal damage and death in the brain.
The group further showed that neurons grown in the laboratory showed increased inflammation when exposed to high levels of glucose, allowing them to shed light on the biological pathways involved.
A review of several studies - written by Margaret Morris, Ph.D., a professor of pharmacology in the School of Medical Sciences of the Unversity of New South Wales - and her colleagues summarised that high sugar consumption correlated with mild cognitive impairment in seniors. It also negatively affects children's cognitive function.
Prof. Morris's group also showed that rats started to experience problems with recognizing places as early as 5 days after starting a high-sugar diet. This was accompanied by widespread inflammation and oxidative stress in the rats' brains.
Research continues to explore the exact mechanisms that sugar employs to affect mental health. In the mean time, reducing your intake of sugar can't do you any harm!