Humans cannot manufacture vitamin C. Although the need for vitamin C (90 mg/d) is thought to be met by diet, studies have found that up to 13.7% of healthy, middle class patients in the United States are depleted.27 Older adults and patients with a poor diet due to drug or alcohol abuse, eating disorders, or affective symptoms are at risk.
Scurvy is caused by vitamin C deficiency and leads to bleeding gums and petechiae. Patients with insufficiency report irritability, loss of appetite, weight loss, and hypochondriasis. Vitamin C intake is significantly lower in older adults (age ≥60) with depression.28 Some research indicates patients with schizophrenia have decreased vitamin C levels and dysfunction of antioxidant defenses.29 Citrus, potatoes, and tomatoes are top dietary sources of vitamin C.
Vitamin A. Although vitamin A activity in the brain is poorly understood, retinol—the active form of vitamin A—is crucial for formation of opsins, which are the basis for vision. Childhood vitamin A deficiency may lead to blindness. Vitamin A also plays an important role in maintaining bone growth, reproduction, cell division, and immune system integrity.30 Animal sources such as beef liver, dairy products, and eggs provide retinol, and plant sources such as carrots, sweet potatoes, and leafy greens provide provitamin A carotenoids that humans convert into retinol.
Deficiency rarely is observed in the United States but remains a common problem for developing nations. In the United States, vitamin A deficiency is most often seen with excessive alcohol use, rigorous dietary restrictions, and gastrointestinal diseases accompanied by poor fat absorption.
Excess vitamin A ingestion may result in bone abnormalities, liver damage, birth defects, and depression. Isotretinoin—a form of vitamin A used to treat severe acne—carries an FDA “black-box” warning for psychiatric adverse effects, including aggression, depression, psychosis, and suicide.
Vitamin D is produced from cholesterol in the epidermis through exposure to sunlight, namely ultraviolet B radiation. After dermal synthesis or ingestion, vitamin D is converted through a series of steps into the active form of vitamin D, calcitriol, which also is known as 25(OH)D3.
Although vitamin D is known for its role in bone growth and mineralization,31 increasing evidence reveals vitamin D’s role in brain function and development.32 Both glial and neuronal cells possess vitamin D receptors in the hippocampus, prefrontal cortex, hypothalamus, thalamus, and substantia nigra—all regions theorized to be linked to depression pathophysiology.33 A review of the association of vitamin D deficiency and psychiatric illnesses will be published in a future issue of Current Psychiatry.
Vitamin D exists in food as either D2 or D3, from plant and animal sources, respectively. Concentrated sources include oily fish, sun-dried or “UVB-irradiated” mushrooms, and milk.
Vitamin E. There are 8 isoforms of vitamin E—4 tocopherols and 4 tocotrienols—that function as fat-soluble antioxidants and also promote innate antioxidant enzymes. Because vitamin E protects neuronal membranes from oxidation, low levels may affect the brain via increased inflammation. Alpha-tocopherol is the most common form of vitamin E in humans, but emerging evidence suggests tocotrienols mediate disease by modifying transcription factors in the brain, such as glutathione reductase, superoxide dismutase, and nuclear factor-kappaB.34 Low plasma vitamin E levels are found in depressed patients, although some data suggest this may be caused by factors other than dietary intake.35 Low vitamin status has been found in up to 70% of older adults.36 Although deficiency is rare, most of the U.S. population (93%) has inadequate dietary intake of vitamin E.1 The reasons for this discrepancy are unclear. Foods rich in vitamin E include almonds, sunflower seeds, leafy greens, and wheat germ.
Patients with depression, alcohol abuse, eating disorders, obsessive-compulsive disorder, or schizophrenia may neglect to care for themselves or adopt particular eating patterns. Deficiencies are more common among geriatric patients and those who are medically ill. Because dietary patterns are linked to the risk of psychiatric disorders, nutritional inquiry often identifies multiple modifiable risk factors, such as folate, vitamin B12, and vitamin D intake.37,38 Nutritional counseling offers clinicians an intervention with minimal side effect risks and the opportunity to modify a behavior that patients engage in 3 times a day.
Psychiatrists should assess patients’ dietary patterns and vitamin status, particularly older adults and those with:
- lower socioeconomic status or food insecurity
- a history of treatment resistance
- restrictive dietary patterns such as veganism
- alcohol abuse.