A diet rich in sugar found in sweet food and drinks may be linked with an increased risk of developing common mental health disorders such as anxiety and depression in men, scientists have said.
Decreasing people's sugar consumption is now considered an interesting public health intervention to reduce rates of obesity, diabetes and other non-communicable diseases. But scientists are also gathering new evidence that consuming less sugar could be beneficial for people's mental health.
Several studies have already shown that higher sugar consumption is linked to a higher depression prevalence. However, scientists could not rule out that mood disorders could lead to higher sugar intake – opening the door to the possibility that the sugary diet-mental health association is the result of poor mental health rather than of high sugar intake.
In a study now published in Scientific Reports, researchers have tried to resolve this issue while they investigated whether a high-sugar diet was positively associated with the risk of mood disorders like depression and anxiety.
The scientists analysed the medical data from 8,087 men and women aged between the age of 39 and 83. This data had been collected over a 22-year period as part of the Whitehall II cohort study, which examined the health of civil servants in the UK. All had completed questionnaires about their diet, lifestyle and mental health. The researchers controlled for a range of factors including health socio-demographic factors and diet-related factors, adiposity and other diseases.
The researchers found that higher levels of sugar intake had an adverse effect on mental health during the follow-up period. They also found that men in the top third of the sample for the highest sugar consumption had a 23% increased risk of developing a common mental health condition after five years.
However, there was no evidence that mental health disorders tend to increase people's sugar intake. The findings indicate that a sugary diet negatively impacts psychological health on the long term, and that reducing people's sugar consumption could bring benefits not only to people's physical health, but to their mental health too.
"We cannot prove our findings using a trial as it would be unethical to expose anyone with lots of sugar and see how they feel after, so we can only work on trying to replicate our analyses in other cohort studies that are representative," lead author Anika Knüppel, from the Department of Epidemiology & Public Health, University College London (UCL), told IBTimes UK.
"We are still not sure what causes depression, but some researchers believe that biological changes are at the root of it. Some of these changes, so-called "biological pathways", could be influenced by sugar and sweet taste. For example, a study in rats found that high sugar and fat diets can reduce a protein called BDNF that influences the growth and development of nerve cells in the brain. This protein is thought to be involved in the development of depression and anxiety."
Other plausible hypotheses to explain the link between sugar and mental health, include the fact that sugary diets could induce a fall in blood glucose level through an exaggerated insulin response. This can influence hormone levels and thus potentially people's moods.
Another theory focuses on the addictive effects of sugar, showing they might be due to dopamine, a brain chemical involved in the reward system. Dopamine is also thought to influence mood, and addiction is itself is associated with a higher risk of developing a mood disorder.
Also possible is that obesity is a mediating factor between a sugary diet and depression, due to psychosocial factors like weight discrimination. More experimental studies in the lab will now be needed to settle this question and to find potential solutions.