Celiac disease is an autoimmune disease of the gastrointestinal system caused by people eating gluten when they are genetically susceptible to the disease. Fatigue and indigestion are common symptoms. Diagnosis is made by small intestine biopsy.
Depression is common among adults with celiac disease. Depression and behavioral disorders are common in adolescents with celiac disease. The treatment is a gluten-free diet and vitamin B-6. Serious depression can appear after the start of the gluten-free diet. There has been a suggestion that the depression could be due to serotonin dysfunction in the brain as the result of tryptophan deficiency.
The authors followed newly diagnosed adolescent patients with celiac disease. Psychiatric symptoms were evaluated and hormonal status (prolactin and thyroid,) tryptophan, tyrosine and large neutral amino acids (LNAA) were tested in the blood after starting a gluten-free diet. The theory was that increased availability of tryptophan could relieve the psychiatric symptoms.
Nine patients around the age of 14-15 were studied in Finland. Periodic psychiatric evaluations were done. Celiac activity was evaluated by testing serum transglutaminase and endomysium autoantibodies. The psychiatric diagnoses included depression, learning disorder, conduct disorder, phobic disorder and attention-deficit hyperactivity disorder.
The patients with depression had significantly higher prolactin levels and significantly lower l-tryptophan/CAA (amino acids which compete with tryptophan for absorption) ratios at the start. Celiac related autoantibody levels decreased to normal after one month on the gluten-free diet. Prolactin and thyroid levels improved in one month.
Most of the psychiatric symptoms improved on a gluten-free diet after three months. At that time serum tyrosine, CAAs and tryptophan had greatly improved. The author’s feel that the study agrees with the idea that psychiatric symptoms could be due to reduced availability of tryptophan to the brain in celiac disease.
The dopamine system could, also, have been involved since tyrosine levels improved with the psychiatric symptoms. Tyrosine is a precursor of dopamine. Increased dopamine activity reduces prolactin levels.
Increased serotonin and dopamine metabolites have been found in the brain after one year on a gluten-free diet.
CONCLUSION: The preliminary results of this study are evidence that, in adolescents with celiac disease, serotonin deficiency due to impaired tryptophan availability, may cause depressive and behavior disorders. The dopamine system could be involved.
NOTE: Other studies have shown that prolactin is a marker for all autoimmune diseases, including lupus and multiple sclerosis.
Tryptophan and 5-OH tryptophan are precursors for the production of serotonin.