Selective serotonin reuptake inhibitors, or SSRIs, are a class of antidepressant drugs that historically succeeded the older antidepressants tricyclics and MAO inhibitors. Unlike the older antidepressants, SSRIs target the mood-enhancing neurotransmitter serotonin specifically. Some individuals do not respond to SSRIs. In some cases, the lack of response is due to a vitamin B12 deficiency.
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Mood disorders, such as major depressive disorder, generalized anxiety disorder and obsessive-compulsive disorder, are linked to low levels of the neurotransmitter serotonin. SSRIs block the serotonin transporter. The serotonin transporter is a molecule that transports serotonin back into the neurons. As serotonin can only work outside the neurons, this process lowers the levels of active serotonin in the brain. By blocking the serotonin transporter, SSRIs thus raise the brain’s levels of serotonin.
Vitamin B12, one of eight B vitamins, is essential to blood formation, regeneration of vitamin B9, or folic acid, DNA synthesis and the proper function of the brain and nervous system. B12 is an essential vitamin. Essential nutrients are molecules the body cannot produce on its own. So they must be supplied in the diet. Even just a small deficiency of vitamin B12 can have drastic effects on mood. Symptoms of a small vitamin B12 deficiency include anxiety, stress, irritability, depression, fatigue and mental confusion. To prevent a vitamin B12 deficiency, take a vitamin supplement or incorporate foods high in vitamin B12, such as beef, liver, seafood, fish, cheese and eggs, into your diet.
Serotonin and B12
SSRIs do not aid in the synthesis of serotonin. They merely prevent the deactivation of serotonin. So, for SSRIs to be effective as antidepressants, the brain must be able to synthesize serotonin, and the available serotonin must be able to promote neuronal activity. Vitamin B12 helps generate the fatty layer of the nerve endings, also known as myelin. The myelin layer must be intact for neuron signals to transmit properly. A vitamin B12 deficiency may impair the myelin layer and prevent proper signal transmission.
Other Causes of SSRI Resistance
Another factor that can affect the proper function of serotonin and SSRIs is a deficiency in the essential fatty acids omega-3. Omega-3 fatty acids fortify the myelin layer surrounding nerve endings. When there are insufficient amounts of omega-3 fatty acids in the brain, serotonin does not function optimally. The essential amino acid tryptophan also plays a role in the proper function SSRIs. The brain synthesizes serotonin from tryptophan. So a diet deficient in tryptophan can prevent SSRIs from working. Fatty fish are good sources of omega-3 fatty acids. Foods rich in tryptophan include turkey, fish, chickpeas, sunflower seeds, buckwheat, tofu, whey protein, flax seeds and flax oil.
- Journal of Clinical Psychiatry; Serum Folate, Vitamin B12, and Homocysteine in Major Depressive Disorder, Part 1: Predictors of Clinical Response in Fluoxetine-Resistant Depression; G. I. Papakostas, et al.; August 2004
- Pediatric Radiology; Retardation of Myelination Due to Dietary Vitamin B12 Deficiency: Cranial MRI Findings; K. Lövblad, et al.; February 1997
- Science Today at the University of California: Myelin: The Insulation that Coats the Brain's Wiring System
- Office of Dietary Supplements, National Institutes of Health: Dietary Supplement Fact Sheet: Vitamin B12
- Journal of Psychiatry and Neuroscience; How to Increase Serotonin in the Human Brain without Drugs; Simon N. Young; November 2007