Physical disorders can negatively affect a person's mental condition, so experts recommend ingesting sufficient nutrients to stimulate the brain and other parts of the body to maintain mental health.
Vitamins tend to be a doctor's first recourse as nutrients that are good for improving mental condition. A number of studies have established that vitamin D and folic acid help deal with depression.
Vitamin D is produced when provitamin D, a substance contained in the skin, is exposed to the sun's ultraviolet rays. In winter, when exposure to sunlight is shorter, it's easy to suffer from insufficient vitamin D.
In regions where sunshine is extremely limited in winter, the number of people suffering from depression increases until early spring.
Hiroshi Kunugi, director of the Department of Mental Disorder Research of the National Center of Neurology and Psychiatry, has written books about the issue, including "Kokoro ni Kiku Seishin Eiyogaku" (Nutrition effective for mental health).
"The theory that a shortage of vitamin D is related to [depression] is widely supported," Kunugi said. "It is also believed that vitamin D improves the functions of neural transmitter substances inside the brain, and works to protect it."
Mushrooms and seafood are rich in vitamin D. Folic acid - a kind of vitamin which is found in large quantities in spinach - has received attention for its benefits for prevention and treatment of depression.
Insufficient folic acid is known to cause such ailments as anemia, and is believed to increase the risk of depression. It is also related to the syntheses of neural transmitter substances, including dopamine and serotonin.
According to researchers, the level of folic acid in the blood of people with depression tends to be lower than that in healthy people.
Natto and liver are also rich in folic acid. An appropriate intake of folic acid is also possible through proper use of commercially available supplements.
In addition to vitamins, the nutrient iron, a major mineral, is also essential for maintaining mental health.
Iron is vital to producing hemoglobin, which transfers oxygen in the blood. If there is insufficient iron, this function of hemoglobin weakens, and less oxygen is carried around the body. This causes iron-deficiency anemia.
Brain function is also affected. Iron deficiency can cause a syndrome in which sufferers feel pain, itching and other senses of discomfort in their legs whenever they lie down. Some people experience sleep disorders due to the symptoms.
There are also cases in which sufferers develop symptoms similar to depression, such as frustration, lack of concentration and loss of interest or attention.
Liver, red meat and fish contain a lot of iron. Women tend to suffer an iron deficiency when they menstruate.
Among women in their 30s to 40s, more than 20 percent are estimated to have low levels of hemoglobin.
It is believed that some cases of postpartum depression, in which women develop such symptoms as depression just after childbirth, are related to a shortage of iron.
"Postpartum depression is caused by changes in hormone balance, and environmental and various other factors," Kunugi said. "An iron deficiency is assumed to be one of them. There aren't many cases in which an increase of iron totally cures postpartum depression, but it's worthwhile taking a blood test to check it out."
Internal organs build up iron reserves. If an iron deficiency lasts too long, reserves begin to decrease. Iron reserves can be measured by examining serum ferritin levels in the blood.
However, excessive iron will adversely affect the internal organs and the health will suffer. A blood test is useful to determine the proper iron intake level.
A serum ferritin test is not included in ordinary health checkups, so you need to consult a doctor if you want to have your blood tested.
There is a theory that the brain and intestines affect each other, so if the intestines are healthy so is the brain.
Recent research points to the possibility that enterobacteriaceae, or the intestinal bacterial group, affects the brain via the intestines, and vice versa.
Irritable bowel syndrome clearly shows that mental stress affects the intestines. Sufferers develop such symptoms as abdominal pains when boarding an overcrowded train.
Although there is no problem with the intestinal tract, sufferers feel abdominal pains or have loose bowels when they become tense. They also may suffer from constipation or a distended abdomen over a long period. It is said that 10 percent to 15 percent of adults suffer from irritable bowel syndrome.
It has become widely known that sufferers have an intestinal bacterial imbalance in many cases.
"There's a report saying that inside the intestines of patients with irritable bowel syndrome, beneficial bacteria such as bifidus have decreased, or detrimental bacteria such as clostridium have increased," Kunugi said. "If the intestinal bacterial imbalance worsens, abdominal pains and other symptoms will occur more often. With increasing stress, the intestinal bacterial balance will deteriorate further. Patients could fall into a vicious cycle."
The condition of intestinal bacteria could be related to depression symptoms.
One report said people who had ingested lactic acid bacteria and bifidus for a month showed a clear reduction of depression or anxiety, compared to those who had not done so.
To maintain a healthy, stress-free condition, it is important to consume fermented food containing lactic acid bacteria.
"I hope that people consume nutritious food that contains beneficial bacteria, such as dietary fiber and oligosaccharides," Kunugi said.
(c) 2016, The Japan News/Yomiuri · Mitsunobu Sato