vitamin B12 and diabetic autonomic neuropathy

A recent Danish study found that vitamin B12 deficiency was associated with diabetic cardiovascular autonomic neuropathy, CAN (see dm b12 def and autonom neurop jdiabcomplic2017 in dropbox, or Hansen CS. J Diabetes Complic. 2017; 31(1); 202)

​Details:

-- 469 type II diabetic patients were screened for CAN by several measures, as well as for peripheral neuropathy.

-- Mean age 59, 60% male, diabetes duration 10 years, 5% excessive alcohol consumption, 12% smokers, BMI 32, blood pressure 132/82, 6% on vitamin B12 supplementation (though 16% in those in the highest B12 quartile), 80% on lipid-lowering drugs, 75% on metformin, 4% on PPIs alone and 10% on the combination with metformin, 40% on insulin

--CAN was measured after a 5-minute supine resting period:

    -- heart rate variability (HRV)

    -- 3 tests assessing cardiovascular autonomic reflexes:

        -- lying-to-standing test

        -- deep breathing test (E/I ratio), a measure of heart rate variation during deep breathing [which is affected by an abnormality in the parasympathetic nervous system]

        -- Valsalva

-- peripheral neuropathy was measured electronically by vibration sensation

Results:

-- B12 level varied from the lowest quartile mean of 190 to the highest quartile of 486 pmol/l

-- serum levels of B12 were significantly lower in those on metformin or proton pump inhibitors, p <0.001.

-- Higher level of B12 were significantly associated with a lower odds ratio of CAN, p=0.04

-- A 25 pmol/l higher level of vitamin B12, adjusted for age, sex, diabetes duration, and alcohol consumption, was associated with:

    -- 6% lower level of CAN diagnosis, odds ratio 0.94 (0.88-1.00, p= 0.034)

    -- an increase of E/I ratio of 0.21% (p= 0.038)
    -- a decrease in resting heart rate of 0.25 bpm (p= 0 .025)

-- no association between B12 levels and decreased vibration/peripheral neuropathy

Commentary:

-- cardiovascular autonomic neuropathy is very common in patients with type II diabetes, ranging in prevalence from 20 to 65% and increasing with length of diabetes. CAN is also an independent predictor of cardiovascular mortality and morbidity. But CAN may well be overlooked clinically until a patient is symptomatic, typically late in its course.

-- Vitamin B12 deficiency is also quite common in diabetics, with estimates from 2-33%,  potentially mediated in part by the use of metformin through a not-so-well understood mechanism. This relationship is both metformin dose-dependent and treatment duration dependent, and may be measurable in as little as 4 months after the onset of use. In addition, the frequent use of proton pump inhibitors may decrease vitamin B 12 levels. Another potential and common mechanism for B12 deficiency in older patients is the age-associated decrease in several digestive enzymes, leading to the inability to liberate B12 from foods thereby decreasing its absorption (studies have found b12 deficiency in 10-25% of elderly, typically asymptomatic).

-- This was an observational study, therefore it is difficult to attribute causation. In addition, there is no compelling evidence that correcting B12 deficiency decreases the likelihood of CAN [one Indian population-based study of healthy elderly showed that B12 supplementation in those deficient led to normalization of decreased heart rate variability (see Sucharita S. Autonoom Neurosci 2012; 168 (1-2); 66)].

--Also, the effect of B12 deficiency on CAN in the study was not particularly large. Part of this is that there were very few patients (0.6% of their population) who they defined as having vitamin B12 deficiency (that being below 125 pmol/l in this study, though many consider the cutpoint to be <148 pmol/l, which translates to <200 pg/ml), so the lowest quartile had lots of patients who were probably not actually B12 deficient. and the likely reason for the low B12 deficiency rates was that the standard clinical practice in that area was to check B12 levels in patients every other year. They did not test for methylmalonic acid or homocysteine, which might have been relevant in those with borderline B12 deficiency (35% had B12 levels between 125 and 250 pmol/l, though others consider borderline to be between 148 and 221 pmol/l​, or 200-300 pg/ml). Also, the fact that the effect was particularly evident for the E/I ratio with deep breathing suggests that a parasympathetic abnormality may predominate, and parasympathetic denervation is in fact typically the first abnormality in CAN, leading to increased sympathetic tone.

-- Of note, several different studies, but not all, show that those with peripheral neuropathy associated with B12 deficiency do improve with B12 supplementation, though the degree of improvement tracks inversely with both the extent and duration of disease.

so, my take on this is that given the clear importance of vitamin B12 for several aspects of health (neurologic, psychiatric, hematologic), and that some of these manifestations may be pretty subtle/very hard to detect early on, I personally think it makes sense to check vitamin B12 levels in the elderly as well as those on metformin and PPIs. And now, perhaps more so in diabetics overall , perhaps when they reach the ripe old age of 50 or so.