Plasma vitamin B12, methylmalonic acid and heart rate variability in healthy young Indian adults

Prevalence of vitamin B12 deficiency in the Indian population is not known, however; it is considered to be higher than in the Western population. Vitamin B12 deficiency is generally diagnosed by the plasma vitamin B12 level. Metabolites of vitamin B12 such as homocysteine (Hcy) and methylmalonic acid (MMA) are considered to be better markers to diagnose vitamin B12 deficiency at the tissue level. Autonomic neuropathy in vitamin B12 deficiency appears to precede other neurological signs. One of the recent techniques to evaluate autonomic neuropathy is heart rate variability (HRV). We evaluated 14 healthy young adults to explore the association of plasma vitamin B12, MMA, and Hcy levels with HRV. Resting lead II ECG was recorded and power spectral analyses were performed. Plasma MMA level was significantly and negatively correlated with the log-transformed low frequency (r = - 0.74, p = 0.002) and total power spectra (r = - 0.55, p = 0.03) of HRV in absolute units. Low frequency (LF) (r = - 0.56, p = 0.03) and high frequency (HF) (r = 0.57, p = 0.03), when represented in normalized units, were also correlated significantly with plasma MMA. In summary, plasma MMA but not vitamin B12 was significantly associated with HRV indices in a young adult population, suggesting that a tissue-level marker of vitamin B12 deficiency is more closely correlated with functional changes.