The United States and over 70 other countries have folic acid food fortification programs. Over-the-counter folic acid supplements alongside fortified foods expose the general population to excessive intake of folic acid, sometimes over the tolerable upper intake level of 1000 µg/day. Folic acid food fortification programs reduce the occurrence of neural tube defects, but excess folic acid intake may have unintended consequences on human health, such as the exacerbation of vitamin B12 deficiency. Pernicious anemia patients in the 1950s and 1960s were treated with folic acid supplements, which successfully resolved their macrocytic anemia, but returned to the clinic with exacerbated symptoms of B12 deficiency, including irreversible cognitive impairment. Today, we understand that pernicious anemia affects the ability to digest and absorb B12. Folic acid ameliorates macrocytic anemia presented by pernicious anemia patients but does not resolve the underlying biochemical B12 deficiency. Diagnosing B12 deficiency can be complex because concentrations of biomarkers of B12 status can vary greatly between patients, so it is important to monitor the impact of folic acid food fortification on the general population.The ‘high folate/low B12 interaction’ is the suspected cause of exacerbation of neurological complications in patients with pernicious anemia prescribed high-dose folic acid supplements. There is circumstantial evidence to suggest the existence of this interaction and the mechanisms involved are yet to be elucidated. A hypothesis has recently been put forth that proposes two primary mechanisms by which excess folic acid depletes circulating holotranscobalamin (holoTC), the “active” form of B12. The first is that folic acid may bind to folate receptors in bone marrow, diverting holoTC to bone marrow to support erythropoiesis. The second is that folic acid interferes with holoTC recycling in renal tubule cells, leading to greater excretion of holoTC. The first aim of this dissertation is to assess the associations of total folate status with biomarkers of B12 status in participants in the 2011-2012 National Health and Nutrition Examination Survey (NHANES) and determine if these associations are specific to the form of elevated folate in serum. Data for methylmalonic acid (MMA), a marker of B12 status, was available for the 2011-2012 NHANES. Mean MMA concentrations by B12 quintile and folate group (non-elevated vs. elevated)were compared. MMA concentrations in the lowest quintile of B12 were higher in the elevated total folate group compared with the non-elevated total folate group. These analyses were repeated for the folate forms 5-methyl THF and folic acid. Similar results were seen for 5-methyl THF, showing greater mean MMA concentration in the elevated folate group compared to the non-elevated folate group in the first quintile of B12. No associations with MMA were observed in the folic acid groupings. The second aim of this dissertation is to determine if the associations between serum folates and B12 biomarkers are modified by B12 status, age, sex, and renal function. Using NHANES 2011-2012 data, separate sub-group analyses were performed for comparison of mean MMA concentrations by B12 quintile and non-elevated and elevated total folate for men and women, age <60 and ≥60 years, and serum creatinine <115 and ≥115 µmol/L. As expected, there were overall greater MMA concentrations observed in the individuals ≥60 years and those with creatinine ≥115 µmol/L. However, the only significant interaction of folate with B12 on MMA was observed in the group with serum creatinine <115 µmol/L. There was no overall difference in MMA concentrations between men and women, nor did sex significantly affect the interaction of folate with B12 on MMA. Additionally, a spline analysis was performed to determine the point below which B12 influences greater accumulation of MMA. Several cut points were identified, but the greatest MMA concentrations are suspected to occur at B12 concentrations <188 pmol/L. The third aim of this dissertation is to examine the effects of a high-dose folic acid supplement (5 mg/d) on biomarkers of folate and B12 status in serum and urine in a single arm 6-week pilot study of ten adults over the age of 60. The purpose of this pilot study was to directly measure outcomes associated with the ‘high folate/low B12 interaction’ and investigate the urinary excretion aspect of the recently proposed hypothesis in vitamin B12 replete participants. No effect of folic acid was observed in serum total B12, serum holoTC, and urinary holoTC after folic acid supplementation. Expected amounts of holoTC excreted were calculated and the actual amount of holoTC excreted at the end of the trial was significantly greater than the expected amount, suggesting the possibility that high-dose folic acid supplementation may increase urinary excretion of holoTC over six weeks. However, the small increase in excretion may not be clinically significant because it was not associated with decreases in serum total B12 or holoTC. The evidence presented in this dissertation suggests excessive intake of folic acid, typically via folic acid-containing supplements, is associated with higher MMA in individuals with poor B12 status and potentially greater excretion of holoTC. Additionally, the identification of a potential inflection point below which the interaction between low B12 and high folate influences the rate of MMA accumulation is a novel finding. This work provides foundation for further investigation of the effects of excess folic acid on vitamin B12 depletion.
Andre J. Smith (Thu,) studied this question.