Vitamin B6, Magnesium and Autism Ranking: Insufficient/Mixed evidence

Risks and Safety


All vitamins and minerals can be hazardous in incorrect doses, and some may interact dangerously with medications already being taken. Therefore, professional advice should always be obtained before embarking on a course of vitamin or mineral supplements.

According to the US Office of Dietary Supplements factsheet on vitamin B6 (2018),

“High intakes of vitamin B6 from food sources have not been reported to cause adverse effects. However, chronic administration of 1–6 g oral pyridoxine per day for 12–40 months can cause severe and progressive sensory neuropathy characterized by ataxia (loss of control of bodily movements). Symptom severity appears to be dose dependent, and the symptoms usually stop if the patient discontinues the pyridoxine supplements as soon as the neurologic symptoms appear. Other effects of excessive vitamin B6 intakes include painful, disfiguring dermatological lesions; photosensitivity; and gastrointestinal symptoms, such as nausea and heartburn.”

According to the US Office of Dietary Supplements factsheet on magnesium (2018),

“Too much magnesium from food does not pose a health risk in healthy individuals because the kidneys eliminate excess amounts in the urine. However, high doses of magnesium from dietary supplements or medications often result in diarrhea that can be accompanied by nausea and abdominal cramping. Forms of magnesium most commonly reported to cause diarrhea include magnesium carbonate, chloride, gluconate, and oxide. The diarrhea and laxative effects of magnesium salts are due to the osmotic activity of unabsorbed salts in the intestine and colon and the stimulation of gastric motility.

“Very large doses of magnesium-containing laxatives and antacids (typically providing more than 5,000 mg/day magnesium) have been associated with magnesium toxicity, including fatal hypermagnesemia in a 28-month-old boy and an elderly man. Symptoms of magnesium toxicity, which usually develop after serum concentrations exceed 1.74–2.61 mmol/L, can include hypotension, nausea, vomiting, facial flushing, retention of urine, ileus, depression, and lethargy before progressing to muscle weakness, difficulty breathing, extreme hypotension, irregular heartbeat, and cardiac arrest. The risk of magnesium toxicity increases with impaired renal function or kidney failure because the ability to remove excess magnesium is reduced or lost”


There are some contraindications (something which makes a particular treatment or procedure potentially inadvisable) for some people. 

According to the US Office of Dietary Supplements factsheet on vitamin B6 (2018),

  • “Vitamin B6 supplements might interact with cycloserine (Seromycin), an antibiotic used to treat tuberculosis, and worsen any seizures and nerve cell damage that the drug might cause.
  • Taking certain epilepsy drugs could decrease vitamin B6 levels and reduce the drugs’ ability to control seizures.
  • Taking theophylline (Aquaphyllin, Elixophyllin, Theolair, Truxophyllin, and many others) for asthma or another lung disease can reduce vitamin B6 levels and cause seizures.”

According to the US Office of Dietary Supplements factsheet on magnesium (2018),

  • “Bisphosphonates, used to treat osteoporosis, are not well absorbed when taken too soon before or after taking dietary supplements or medications with high amounts of magnesium.
  • Antibiotics might not be absorbed if taken too soon before or after taking a dietary supplement that contains magnesium.
  • Diuretics can either increase or decrease the loss of magnesium through urine, depending on the type of diuretic.
  • Prescription drugs used to ease symptoms of acid reflux or treat peptic ulcers can cause low blood levels of magnesium when taken over a long period of time.
  • Very high doses of zinc supplements can interfere with the body’s ability to absorb and regulate magnesium.”

If you have concerns about your diet or your child’s diet, you should seek advice from a responsible health professional such as a GP or pharmacist. This may lead to a referral to a dietitian, in particular one with experience of working with individuals on the autism spectrum.


Acid reflux (burning feeling in the chest caused by stomach acid travelling up towards the throat); dermatological lesion (abnormal lump, bump, ulcer, sore or coloured area on the skin); diuretics (medications designed to increase the amount of water and salt expelled from the body as urine); gastric motility (movements of the digestive system); heartburn (another term for acid reflux); hypermagnesemia (high level of magnesium in the blood); hypotension (low blood pressure); ileus (lack of movement somewhere in the intestines); neuropathy (damage to the nerves in the arms and legs, hands and feet); osmotic (tendency of a fluid to pass through a membrane into a solution where the solvent concentration is higher); photosensitivity (sensitivity to light); nausea (feeling sick); osteoporosis (condition in which bones lose their strength); peptic ulcers (open sores that develop on the lining of the stomach); renal function (kidney function).

21 Dec 2018
Last Review
01 Dec 2018
Next Review
01 Dec 2021