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Emerging link between sugar and depression

Emerging link between sugar and depression

Researchers have long looked for a link between elevated sugar intake and depression. Happiest Health digs deeper
Illustration of a person eating cake
Representational image | iStock

Do you find yourself craving ice cream, pastries, or chocolates when you’re feeling low? Or reaching for aerated, sugary drinks to keep yourself alert during a night shift at work?

The habit of consuming sugary foods and beverages can induce a positive feeling in that moment, but some experts worry that there’s a likelihood of it having the opposite effect on your mental health in the long term.

While researchers still don’t know if excess sugar intake causes anxiety and depression, or whether persons suffering from these common mental disorders (CMDs) are more inclined to consume a high-sugar diet, the association of the two is well established.

A 2017 UK study that analysed responses of sugar intake from sweet foods and beverages and occurrence of CMDs found that individuals consuming more than 67gm of sugar a day had a 23 per cent increase in chances of developing CMDs after five years, compared with those consuming less than 39.5gm of sugar a day.

Led by researcher Anika Knüppel, from the department of epidemiology and public health at the University College of London (UCL), the study analysed inputs from over 10,000 people from the UK – 67 per cent men and 33 per cent women, aged between 35 and 55 – over a period of 22 years (from 1983 to 2013).

The study found the incidence of developing CMDs to be higher in men but noted that there was a chance of being depressed again with a mood disorder in five years in both men and women.

While the study was limited in that it did not consider factors such as other health conditions, health-related behaviours, socio-demographic factors, obesity, and other diet-related factors, it does throw light on the link between sugary foods and beverage consumption, and CMDs.

“The relation between sugar and mental health is bidirectional,” says Dr Bharath Holla from the department of psychiatry at the National Institute of Mental Health and Neurosciences (NIMHANs), Bengaluru. “It is still an area of debate whether a high sugar diet makes a person anxious or depressive, or if anxious or depressive persons consume high sugar diets.”

Dr Holla, who specializes in addiction and other related behaviours, says that people can develop an addiction to sugar in the same way they do to illicit drugs such as cocaine. Once they experience a high, they want more – and over time, if the habit continues, an individual might get addicted to sugar.

“Sugar is linked to satiety,” Dr Holla says. “Having a sweet dish or dessert at the end of a meal creates a stop signal in the brain which makes you feel satiated.”

Others believe there are underlying factors that contribute to mental health conditions, and higher intake of sugary food and beverages might act as a catalyst for the incidence of mental disorders. People with target-based jobs or those working in night shifts tend to consume more sugary and caffeinated beverages, says Dr Mohit Sharma, a Chandigarh-based doctor specializing in diabetes and hypertension.

The correlation between the behaviours of consuming excessive sugary beverages, which can add an average of 35-40gm of excess sugar to one’s diet, and stress-inducing work behaviour, is what might be driving the high incidence of elevated sugar intake and depression.

“High sugar consumption does not cause depression or other mental disorders,” says Dr Sharma. “It is caused if there is any other associated factor that has a potent influence on mental health along with sugary foods.”

He said that for the UCL study to blame sugar as the only culprit for mental health conditions was wrong. Adding that different results might be had if different populations are studied, Dr Sharma called for more inclusive research to be done in this area.

While some studies have also shown that high-sugar-containing foods might be linked to aggravating the inflammatory markers that in turn can increase the risk of developing depression, a stressful work environment and sedentary lifestyle could just as easily be the underlying factors of mental health disorders.

There is also some evidence to suggest that people who consume high amounts of sugar are at risk of developing mental health disorders due to changes in the physiology of the brain.

In a study published in the November 2020 edition of Springer Nature, the researchers analysed brain MRI scans of 2,000 participants and found a difference in the subcortical regions of the brain, especially in obese persons.

This region of the brain is linked with different functions, such as modulating hormonal, emotional and pleasure states, leading the researchers to believe that there could be a link with obesity in the incidence of mental health disorders. “If a person is vulnerable to conditions that can affect mental health and consumes high sugar, they are at high risk of developing mental disorders,” said Dr Holla, who was a part of the study.

Another study from Columbia University’s department of psychiatry in 2015 suggested that a diet that spikes sugar levels in the blood could be a risk factor for depression in post-menopausal women.

Led by researcher James E Gangwisch, the study reported on a possible mechanism in which a high glycemic index (GI) diet – a diet that spikes the blood sugar level – could lead to insulin resistance, which is associated with neurological deficits that are like those reported by individuals suffering from major depression.

Another possible mechanism for sugar being linked to depression and other CMDs is the repeated spikes in blood sugar that cause insulin levels in the body to surge. Researchers have theorised that insulin lingers on after counteracting excess sugar in the body when there are repeated sugar spikes. This leftover insulin causes blood sugar levels to dip even when they are normal, bringing down the levels of brain sugar as well.

Our brains can show cognitive impairment, mood and behavioural changes, and fatigue when there is an absence of sugar. This is understood to be a mechanism by the brain to get the body to load up on sugars once again.

Moreover, with a drop of brain sugar levels, it produces hormones such as adrenaline, cortisol, glucagon and growth hormones that can manifest anxiety, irritability and hunger.

While higher sugar intake might not be the cause for depression, the underlying conditions causing both might be linked. Experts, therefore, say it is not a bad idea to moderate sugar intake and watch one’s sugar source, even if it hasn’t been found to be a major factor contributing to increased risk of developing common mental health disorders.

UK’s National Health Service (NHS) recommends no more than 30gm of free or added dietary sugar for an adult, 24gm for children aged seven to 10 years, and 19gm for children aged four to six years. However, for children below four years of age, NHS and experts recommend avoiding any sugary or sweetened food or drinks.

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