Beriberi is caused by a deficiency of thiamine (vitamin B1), which in turn causes neurological, mental, and cardiovascular problems.

Symptoms of beriberi range from mild to severe.

Mild symptoms include fatigue, irritation, slow learning and confusion, poor cold tolerance, nausea, vomiting, and whiteheads on the face or upper torso.

Severe symptoms include memory loss, heart pain, weight loss, abdominal and heart discomfort, poor digestion, gas, diarrhea, constipation, extreme fatigue, mood swings, mental confusion, tachycardia (rapid heart rate), and heart failure, and if left untreated, can even result in death.

Parasites, gastrointestinal or liver disease, food allergies, and/or severe stress can all be causes or co-factors of beriberi.

Beriberi is divided into two classifications - primary beriberi and secondary beriberi.

Primary beriberi is caused by the inadequate intake of vitamin B1 through food. It occurs most often in people who eat highly refined and processed foods. It is especially prevalent in people who subsist on polished (white) rice, as vitamin B1 is lost in the milling process that produces white rice.

Secondary beriberi is related to the loss of B1 due to poor utilization of the nutrient in the body due to such factors as liver disease, gastrointestinal problems, alcoholism and/or drug addiction, pregnancy, hyperthyroidism (overactive thyroid), breast-feeding, fever, stress (emotional and physical), genetic predisposition, and impaired absorption, such as with diarrhea, parasites, gastrointestinal loss of friendly bacteria, damage to the lining of the gastrointestinal tract by drugs, alcohol, stress, parasites, food allergies, celiac disease (wheat intolerance), or other gut problems.