In certain cases, psychological or behavioral problems can be caused by some type of imbalance or problem in the body. As stated by Professor Erich Kasten, who studies medical psychology, “many physical ailments can surreptitiously erode the psyche. For example, inflammation from infectious and chronic disorders can spawn depression. Sadness and lethargy may also result from hormone imbalances or nutrient deficiencies. Anxiety symptoms can be a sign of allergies or an overactive thyroid gland. And something as simple as a lack of water or iron can impair the ability to learn, remember and plan.” (Kasten, 2011, p. 53)

Scientists have known since 1950 that people who reduce their calorie intake by 50% can experience depression, apathy, slower movement, and other detrimental cognitive effects. (Beil, 2011) This may be one of the reasons depression and eating disorders seem to go hand in hand. Both feed off one another. Certain nutrient deficiencies can further hamper things. Calcium, for instance, is crucial to a healthy brain: nerve cells need it to create the electrical impulses used to communicate with one another. Here are some other ways in which nutrition has been linked to proper mental health:

  • Zinc deficiency has been linked to depression. In the brain, zinc seems to concentrate in glutamatergic neurons, which increase brain activity and are involved in neuroplasticity. “Those neurons feed into the mood and cognition circuitry,” says psychiatry professor Krista L. Lanctot. (Rodriguez, 2015)

  • Low magnesium has been linked to anxiety and depression, and seems to create alterations in gut microbiota that are linked to inflammation. (ibid)

  • Iron deficiency has been linked to cognitive deficits in both children and adults (ibid), because it impedes neurotransmission and cell metabolism. (Red cells need it to carry oxygen). Around 1 in 4 pregnant women suffer from iron deficiency, and in the developed world, about 10% of women overall are deficient. (Kasten, 2011)

So hunger and poor nutrition can compromise the brain. So does dehydration, which can cause inattention and ADHD-like symptoms in children. Without enough water, brain cells can shrivel up, shrinking brain tissue and enlarging the spaces within the brain (called ventricles) thus making it harder to process information. “In young adults,” Kasten says, research suggests that “even mild dehydration leading to a loss of 2 to 3 percent of body weight can significantly impair cognitive capacities such as short-term memory attention and ability to solve math problems.” So it doesn’t take much to cause impairment. “Even under ordinary conditions,” he continues, “just having a drink could help you think – at least if you are a kid. In a 2009 study psychologists Caroline J. Edmonds and Ben Jeffes of the University of East London found that giving mildly dehydrated six- and seven-year-olds a glass of water before a test improved their scores. In another study of seven- to nine-year-olds, additional water similarly boosted performance in an assessment of visual attention.” (Kasten, 2011, pp. 56-57 If something so minor can have a measurable effect, it makes you wonder how many other environmental issues (lack of exercise, caffeine intake, etc.) might be contributing to the symptoms of the millions of kids in this country being diagnosed with ADHD.

Diseases that impact the brain

Genetic or physical conditions that affect the balances of hormones in the body can also spur on mental illness. A drop in estrogen, in particular, can really affect emotions. The thyroid gland, which is located in the neck, produces hormones that serve a variety of functions; everything from aiding in digestion to regulating our moods. Therefore physical conditions that impact the functioning of this system can in turn alter one’s moods and emotions.

A perfect example of this is hyperthyroidism, which affects around 1% of the population. Because the illness impacts the gland which secretes hormones, which in turn act on our brain, the condition can lead to significant physical and mental distress–so much so that a person with the disorder has a sevenfold increased risk of suffering from a mood disorder. There’s also porphyria, a group of rare metabolic disorders which affect molecules that carry oxygen in red blood cells. Without enough oxygen the brain cannot function optimally, increasing the risk of depression. (ibid)

Extreme cold can also have an effect. One of the functions of the thyroid gland is to regulate body temperature. So during long-term exposure to cold, these hormones are so busy trying to keep the body warm that the brain–which also relies on these substances – can get shortchanged. (Anthes, 2010) This may be one of the reasons that colder climates tend to see a slight uptick in depression during the winter months.

Chronic illnesses such as diabetes may also affect temperament, because people who have trouble metabolizing glucose have less energy to devote to self-control and therefore become more aggressive. Studies have found that the more severe a diabetics symptoms, the more violent and unforgiving that person was judged to be by both himself and others. (Schreiber, 2011)