Prof. Dr. med. vet. K. Pietrzik, Institut für Ernährungs- und Lebensmittelwissenschaften [Institute for Nutrition and Food Sciences], University of Bonn
“As part of a randomized, placebo-controlled study, B-vitamins (25 mg vitamin B6, 2.5 mg vitamin B9 plus 1 mg vitamin B12 daily) were administered to 238 diabetics to explore whether these vitamins slow the progression of damage to the kidneys caused by diabetes (diabetic nephropathy) and prevent cardiovascular diseases (1).
The study was conducted in Canada between 2001 and 2007. The authors considered the fortification of basic foodstuffs with folic acid, which has been mandatory in Canada since January 1, 1998, to be the reason behind high levels of vitamin B9 (folate) in all participants at baseline and very high levels at the end of the trial. In addition, participants were allowed to take multivitamin preparations during the study, although no the publication did not provide precise information on the amounts involved. The study comes to the conclusion that the consumption of B-vitamins impairs kidney function and significantly increases the risk of vascular events (e.g. stroke and myocardial infarction).
This study design involved potential overlying effects of fortification with folic acid, possible intake of multivitamin preparations and preventive medication for vascular diseases. This study is therefore not suitable to investigate the usefulness of B-vitamin administration for the prevention of cardiovascular diseases. Accordingly, no positive result could be expected.
Thus a further preventive effect on cardiovascular diseases of additional vitamin administration was hardly likely following a general improvement in folate status due to fortification. This was especially improbable because all the participants were receiving optimal preventive medication for heart conditions, the effects of which are comparable with the lowering of homocysteine levels described for folate.
The significant increase in vascular events after administration of B-vitamins was just as unexpected. However, closer analysis reveals that the number of these cases rose suddenly in the B-vitamin group right at the start of the trial and after only six months (!) was higher by ten cases (107 vs. 117) than in the placebo group. The difference remained more or less the same over the rest of the study up to the 36th month, and the gap actually narrowed at the end of the study to eight cases (45 vs. 53). It was also remarkable that in the first six months there was hardly any increase in risk in the placebo group, while the risk developed in parallel with the B-vitamin group during the rest of the study (always with the ca 10-case difference due to the sudden increase in cases in the B-vitamin group in the first six months).It is regrettable that the study's authors do not comment on these problematical statistical findings.”
Bonn, May 2010