A Guide To Nutritional Supplements For Patients With Diabetes
Understanding The Effects Of Vitamin Supplements
• Thiamin (vitamin B1). Thiamin is the active form of thiamine pyrophosphate, which functions as a cocarboxylase. It is required for the oxidative carboxylase of pyruvate to form active acetate and acetyl coenzyme A. It is also required for the oxidative carboxylase of other alpha-keto acids such as alpha-ketoglutaric acid into keto-carboxylase derived from the amino acids methionine, threonine, leucine, isoleucine and valine. Allicin, a substance found in onions and garlic, combines with thiamine and renders it more absorbable. Thiamine pyrophosphate (TPP) is involved in the oxidation pathway and may be responsible for the energy required for nerve conduction.
Diabetic patients, who would normally have a high intake of carbohydrates, need an increase in the amount of thiamine in their diet. The recommended daily allowance (RDA) is 1.0 to 2.4 mg per day. Therapeutic levels of thiamin for patients with diabetes should be in the range of 60 mg per day in divided doses. Many nutriceutical manufacturers provide multivitamin mineral supplements with thiamine in the 60 mg per day therapeutic range.
There is very little evidence of thiamine toxicity. In monkeys, the lethal dose is greater than 350 mg/kg body weight.
• Riboflavin (vitamin B2). Riboflavin is essential in the activation of vitamin B6 and is involved in converting tryptophan to niacin. Riboflavin is essential for the production of corticosteroids and in the regulation of gluconeogenesis and thyroid enzyme regulation. Vitamin B2 is the component of two major energy enzymes: flavin mononucleotide and flavin adenine dinucleotide. Vitamin B6 is also important in glucose metabolism. Exercise uses glucose stores and can dramatically alter levels of the active coenzyme form of B6.5
The RDA for B2 is 1.2 to 1.6 mg per day and is 1.5 to 1.7 mg/day during pregnancy/lactation. Therapeutic levels of vitamin B2 should be in the range of 60 mg per day. No toxicity due to riboflavin has been found.
• Vitamin B6 (pyridoxal-5-phosphate). Vitamin B6, in its active form, is involved in the transamination of ammonia groups to other amino acids. It is also involved in the deamination or removal of amino acids. It can also be useful as an energy source and in the decarboxylation process for the removal of carboxyl (C00H) groups from certain amino acids to form another compound. It is required in the synthesis of neurotransmitters such as serotonin, norepinephrine and histamine from tryptophan, tyrosine and histamine.
The RDA requirement for Vitamin B6 is 2 to 2.2 mg per day. It is 5 to 6 mg/day during pregnancy/lactation. The therapeutic level of vitamin B6 is at least 60 mg per day.
Toxicity with vitamin B6 has been reported in one case in which a dosage of 200 mg/per day was administered and resulted in peripheral neuropathy. Normally, it would take a dosage of 225 g per day for a few months in order to cause toxic symptoms consisting of numbness and tingling in extremities. The symptoms usually disappear once the patient discontinues the B6 but may linger for a few months if the symptoms are severe. If the patient is on L-dopa for Parkinson’s disease and takes vitamin B6, the vitamin will convert the L-dopa into dopamine outside the blood/brain barrier. This will render the L-dopa ineffective because dopamine cannot pass the blood/brain barrier.
If the patient is on Sinemet® (a combination of L-dopa and carbidopa), B6 may actually have a synergistic effect. Carbidopa stops conversion of L-dopa outside the blood/brain barrier. The vitamin B6 would then cross the blood/brain barrier along with the unchanged L-dopa. Once inside the blood/brain barrier, the B6 would then convert the L-dopa into dopamine where the brain could then effectively use it.