Systematic Review of Observational Studies with Dose-Response Meta-Analysis between Folate Intake and Status Biomarkers in Adults and the Elderly

Folic acid: friend or foe in cancer therapy

Folic acid plays a crucial role in diverse biological processes, notably cell maturation and proliferation. Here, we performed a literature review using articles listed in electronic databases, such as PubMed, Scopus, MEDLINE, and Google Scholar. In this review article, we describe contradictory data regarding the role of folic acid in cancer development and progression. While some studies have confirmed its beneficial effects in diminishing the risk of various cancers, others have reported a potential carcinogenic effect. The current narrative review elucidates these conflicting data by highlighting the possible molecular mechanisms explaining each point of view. Further multicenter molecular and genetic studies, in addition to human randomized clinical trials, are necessary to provide a more comprehensive understanding of the relationship between folic acid and cancer.

Intended and Unintended Benefits of Folic Acid Fortification-A Narrative Review

Inadequate folate intake during pregnancy is the leading cause of the development of neural tube defects (NTDs) in newborns. For this reason, mandatory fortification of folic acid, a synthetic, easily bioavailable form, in processed cereals and cereal products has been implemented in the US since 1 January 1998 to reduce the risk of NTD in newborn children. This report aimed to review the literature related to the impact of mandated folic acid fortification on the intended and unintended benefits to health. Potential adverse effects were also discussed. We searched Pubmed, Google Scholar, Embase, SCOPUS, and Cochrane databases for reports. About 60 reports published between January 1998 and December 2022 were reviewed, summarized, and served as background for this review. The intended benefit was decreased prevalence of NTDs, while unintended benefits were reduction in anemia, blood serum homocysteine, and the risk of developing cardiovascular diseases. Potential issues with folic acid fortification are the presence of unmetabolized folic acid in circulation, increased risk of cancer, and the masking of vitamin B-12 deficiency. From a health perspective, it is important to monitor the impact of folic acid fortification periodically.

The associations of dietary folate and serum folate with lipid profiles: findings from the national health and nutrition examination survey 2011-2016

BACKGROUND

Folate is considered to be related to lipid metabolism. With the increasing numbers of folic acid fortification nations, the associations of dietary folate and serum folate with lipid profiles deserve more attention and are worth further study.

METHODS

US adults aged ≥ 20 years from the National Health and Nutrition Examination Survey (NHANES) were evaluated. Participants taking folic acid supplements were excluded. The multivariate linear regression model and smooth curve fitting were applied to assess the associations. The segmented regression model was employed to examine the threshold effect of nonlinear relationships.

RESULTS

Our cross-sectional study included 3706 participants in total. There was a negative relationship between serum folate (log transformed) and triglycerides (β = -0.223, 95% CI: -0.337, -0.110) and low-density lipoprotein cholesterol (LDL-C) (β = -0.152, 95% CI: -0.296, -0.007) and a positive relationship between serum folate (log transformed) and high-density lipoprotein cholesterol (HDL-C) (β = 0.090, 95% CI: 0.033,0.146). There was a negative association between dietary folate (log transformed) and total cholesterol (TC) (β = -0.299, 95% CI: -0.465, -0.134) and LDL-C (β = -0.266, 95% CI: -0.409, -0.123). A nonlinear relationship was found between dietary folate (log transformed) and HDL-C. Threshold effect analysis showed that the inflection point was 377.57 ug. Within the inflection point, the β-coefficient of HDL-C was 0.105 (95% CI: 0.018, 0.192); beyond the inflection point, there was no relationship (β = -0.067, 95% CI: -0.162, 0.028).

CONCLUSIONS

Optimal dietary folate and high serum folate were associated with favorable lipid profiles. Dietary folate, in the recommended 300-400 ug/d, had a beneficial effect on improving lipid profiles.

Relationship between intake and plasma concentrations of vitamin B12 and folate in 873 adults with a physically active lifestyle: a cross-sectional study

BACKGROUND

Vitamin B12 and folate function as co-factors in pathways used during physical activity. Physical activity may therefore increase vitamin requirements, leading to a risk of deficient plasma concentrations. We aimed to investigate the relationship between intake and plasma concentrations of vitamin B12 and folate in physically active adults, as well as identify other determinants of vitamin B12 and folate plasma concentrations.

METHODS

The study population consisted of 873 adults (528 men and 345 women), aged 19-78 years, who participated in a 4-day walking event. The relationship between intake and plasma concentrations of vitamin B12 and folate was assessed using correlation and linear regression analyses. In addition, potential other determinants (sex, age, body mass index, energy intake and physical activity) of vitamin plasma concentrations were investigated.

RESULTS

Significant positive correlations were observed between intake and plasma concentrations of vitamin B12 [Pearson's correlation coefficient = 0.15; 95% confidence interval (CI) = 0.08-0.21] and folate (Pearson's correlation coefficient = 0.18; 95% CI = 0.12-0.25). In addition to vitamin intake, sex, age and energy intake were also determinants of both vitamin B12 and folate plasma concentrations in multivariable regression models.

CONCLUSIONS

The results suggest a positive association between intake and plasma concentrations for both vitamin B12 and folate in physically active people. By contrast to our hypothesis, physical activity was not a determinant of vitamin B12 and folate plasma concentrations. However, sex, age and energy intake were found to be determinants. Thus, when studying the relationship between intake and plasma concentrations of vitamin B12 or folate, these factors should be taken into account.

Blood Flow Deficits and Cerebrovascular Changes in a Dietary Model of Hyperhomocysteinemia

Elevated homocysteine in the blood, or hyperhomocysteinemia, is a recognized risk factor for multiple causes of dementia including Alzheimer’s disease. While reduction of homocysteine levels can generally be accomplished in a straightforward manner, the evidence regarding the cognitive benefits of this approach is less clear. To identify adjunct therapeutic targets that might more effectively restore cognition, the present series of experiments characterizes early and later cerebrovascular changes in a model of hyperhomocysteinemia. Sex-balanced groups of adult C57BL/6J mice were administered a diet deficient in vitamins B6, B12, and B9 (folate) and supplemented with excess methionine. They were subsequently assessed for changes in cerebral blood flow, memory, blood–brain barrier permeability, and selected vascular-associated genes. Blood flow deficits and barrier permeability changes occurred alongside changes in memory and in genes associated with metabolism, endothelial nitric oxide signaling, barrier integrity, and extracellular matrix remodeling. Significant sexually dimorphic responses to the diet were also detected. Taken together, these data deepen our understanding of a major contributor to dementia burden.