Estimating Vitamin C Intake Requirements in Diabetes Mellitus: Analysis of NHANES 2017-2018 and EPIC-Norfolk Cohorts

A cross-sectional observational study of the association between biochemistry profiles and the risk of age-related macular degeneration

This study aimed to explore the relationship between biochemical profiles and the risk of age-related macular degeneration (AMD) through a cross-sectional observational analysis. We examined data of U. S. population from the 2005-2008 National Health and Nutrition Examination Survey (NHANES) database. Student's t-test, multivariable logistic regression, Pearson's correlation, restricted cubic spline (RCS) model, and linear regression were applied to analyze the underlying relationship between biochemical profiles and the AMD risk, through comparing data between the non-AMD and AMD subgroups. Multivariable logistic regression, adjusted for age and demographic factors, showed no significant associations between the AMD risk and the levets of specific biochemical parameters (P > 0.05). Pearson's correlation revealed a positive linear relationship between age and total bilirubin, uric acid in the non-AMD subgroup (P < 0.05), but no such liner association was found in the AMD subgroup (P > 0.05). The RCS model confirmed no non-linear relationships presented between these variables in the AMD subgroup. In addition, without age adjustment, significant associations were found between total bilirubin, uric acid, and the AMD presence (P < 0.05). Biochemical profiles, after adjusting for age, did not significantly influence the AMD risk. However, total bilirubin and uric acid might potentially be related to the AMD presence. Our findings suggest a need for further research to clarify the role of these biomarkers in AMD development.

The pharmacology of vitamin C

Ascorbic acid, the reduced form of vitamin C, is a ubiquitous small carbohydrate. Despite decades of focused research, new metabolic functions of this universal electron donor are still being discovered and add to the complexity of our view of vitamin C in human health. Although praised as an unsurpassed water-soluble antioxidant in plasma and cells, the most interesting functions of vitamin C seem to be its roles as specific electron donor in numerous biological reactions ranging from the well-known hydroxylation of proline to cofactor for the epigenetic master regulators ten-eleven translocation enzymes and Jumonji domain-containing histone-lysine demethylases. Some of these functions may have important implications for disease prevention and treatment and have spiked renewed interest in, eg, vitamin C's potential in cancer therapy. Moreover, some fundamental pharmacokinetic properties of vitamin C remain to be established including if other mechanisms than passive diffusion governs the efflux of ascorbate anions from the cell. Taken together, there still seems to be much to learn about the pharmacology of vitamin C and its role in health and disease. This review explores new avenues of vitamin C and integrates our present knowledge of its pharmacology. SIGNIFICANCE STATEMENT: Vitamin C is involved in multiple biological reactions of which most are essential to human health. Hundreds of millions of people are considered deficient in vitamin C according to accepted guidelines, but little is known about the long-term consequences. Although the complexity of vitamin C's physiology and pharmacology has been widely disregarded in clinical studies for decades, it seems clear that a deeper understanding of particularly its pharmacology holds the key to unravel and possibly exploit the potential of vitamin C in disease prevention and therapy.

A Systematized Review of the Relationship Between Obesity and Vitamin C Requirements

Obesity rates have increased globally in recent decades. Body weight is used as a modifiable factor in determining vitamin requirements. Accordingly, vitamin C requirements are volumetrically scaled from data for healthy weight males to other age- and sex-based categories. Likewise, it is possible that increases in body weight due to obesity may affect vitamin C needs. A systematized literature review was performed to summarize evidence on whether obesity affects vitamin C intake or status. The literature was also scanned for potential mechanisms for the relationship. Many observational studies showed that vitamin C status is lower in overweight and obese children and adults; this may be explained by lower vitamin C intakes. Nevertheless, a reanalysis of carefully conducted intervention studies has demonstrated a lower vitamin C status in participants who were overweight or obese when given the same dose of vitamin C as subjects of normal weight. Several mechanisms have been proposed to potentially explain why vitamin C status is lower in people with obesity: changes in vitamin C partitioning between lean and adipose tissue, volumetric dilution, metabolic alterations due to obesity, and gut microbial dysbiosis. Depletion-repletion or pharmacokinetic studies that include individuals of diverse body weights and ages would be helpful to further investigate whether obesity increases requirements for vitamin C. The current evidence base supports a lower vitamin C status in people who are overweight or obese; however, the association may be attenuated by lower vitamin C intakes.