Several observational studies have shown that patients with type 2 diabetes have low levels of B vitamins, partially induced by metformin. Hence the interest in assessing the clinical implication of possible supplementation.
Low levels of thiamine (vitamin B1) are attributable to an increase in its urinary excretion and because it plays a role in improving endothelial cell function it may be important in delaying the vascular complications of diabetes. A pilot study involving 40 randomised participants taking thiamine doses of up to 300 mg/day was conducted in 2011 to assess whether such therapy could reverse microalbuminuria in type 2 diabetes with nephropathy. The researchers found a regression of urinary albumin excretion in the treatment group and therefore concluded that thiamine supplements may provide better therapy for early-stage diabetic nephropathy.
Much discussed is the role of niacin (vitamin B3) in cholesterol management in type 2 diabetes after two randomised trials, Aima-High and Hps2-Thrive, showed that patients taking niacin had a significant excess of serious adverse events associated with the gastrointestinal system, myopathy and skin ulcers. The most recent study, conducted in 2014, exploring extended-release niacin in patients with type 2 diabetes on statins, found that it increased Hdl cholesterol concentrations among those with target Ldl cholesterol levels. The authors of the paper therefore concluded that this supplement may provide a benefit on the risk of cardiovascular disease in type 2 diabetes.
Biotin (vitamin B8), by virtue of its regulatory action on insulin secretion and its tolerability at pharmacological doses, is perhaps the vitamin of the group with the most data available. Recently, a study with a daily dose of 61.4 μmol biotin or placebo for 28 days in 18 subjects with type 2 diabetes and 15 non-diabetics found that the vitamin significantly reduced plasma concentrations of triacylglycerol and very low density lipoprotein cholesterol. Alongside these findings, however, the authors found no significant effects of biotin on glucose and insulin in either group and this work is also inconclusive on the role of biotin in the management of type 2 diabetes.
High plasma homocysteine concentrations have been linked to an increased risk of diabetic complications. The Hope study (Heart outcomes prevention evaluation) concluded that daily vitamin B therapy reduced homocysteine concentrations by 25%. In the same year, 2010, in a multicentre, randomised, double-blind study involving 238 participants with diabetic nephropathy, participants received either a high-dose vitamin B supplement (vitamin B9 2.5 mg/day, vitamin B6 25 mg/day, vitamin B12 1mg/day) or placebo. The results indicate that although the patients on the treatment significantly lowered plasma homocysteine levels, there was a rapid decline in kidney function and increased rates of vascular events such as myocardial infarctions and strokes. Overall, it can be said that, over time, enthusiasm for the role played by homocysteine in the complications of diabetes has waned because studies have shown unconvincing and sometimes contradictory results.
It is still unclear whether vitamin B supplements alter pain perception in diabetics with peripheral neuropathy. Alongside glycaemic control, vitamin B12 is nevertheless the most commonly used supplement in the management of diabetic neuropathy, and a recent prospective, double-blind, controlled study evaluated for the first time the isolated effect of methylcobalamin with clearly defined dosage, duration, molecular form and mode of administration.
Specifically, all treated patients on metformin therapy for at least 4 years, diagnosed with peripheral and autonomic neuropathy and initial B12 levels below 400 pmol/L, received supplementation with oral methylcobalamin 1,000 µg/day for 12 months. Again, methylcobalamin induced improvements in nerve conduction parameters, which is consistent with its action on myelin regeneration and synthesis, and showed an effect on pain reduction.
A review analysed five studies with a total of 348 participants, which varied in terms of the vitamin B compound, dose and duration of treatment used. The results concluded that it was still unclear whether vitamin B supplements altered pain intensity or neuropathic damage, either in the short or long term in people with diabetic peripheral neuropathy; only two studies reported the absence of adverse events.
Bibliography
folic acid and vitamin B12 supplementation in subjects with type 2 diabetes mellitus: a multi-arm randomized controlled clinical trial. Complementary Therapies in Medicine, 22 July 2020, volume 53.
Implication of homocysteine in diabetes and impact of folate and vitamin B12 in diabetic population. Diabetes & metabolic syndrome: clinical research & reviews, 13 December 2016, volume 11, supplement 1.
Vitamin supplements in type 2 diabetes mellitus management: a review diabetes & metabolic syndrome: clinical research & reviews, 12 April 2017, volume 11, supplement 2.
Vitamin B12 supplementation in diabetic neuropathy: a 1-year, randomized, double-blind, placebo-controlled trial. Nutrients. 2021 Jan 27;13(2):395.
Vitamin B for treating diabetic peripheral neuropathy – a systematic review. Diabetes & metabolic syndrome: clinical research & reviews, 18 July 2021, volume 15, Issue 5.
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