Biological variation of ascorbic acid and α-tocopherol

Area of Science:

• Nutritional Biochemistry
• Clinical Chemistry
• Epidemiology

Background:

• Free radicals are implicated in various diseases, including cancer, ischemic heart disease, and stroke.
• Epidemiological studies often correlate plasma antioxidant vitamin levels with disease risk.
• Previous research frequently overlooks significant intra-individual variability in antioxidant concentrations.

Purpose of the Study:

• To investigate the weekly and monthly variability of ascorbic acid and alpha-tocopherol plasma levels.
• To assess the significance of intra-individual variation in antioxidant concentrations.
• To compare the critical differences required for detecting significant changes in serial measurements for both vitamins.

Main Methods:

• Study involved 12 healthy volunteers (4 women, 8 men) aged 23-45 years.
• Plasma vitamin levels were measured over 12 weeks using high-performance liquid chromatography.
• Intra-individual coefficients of variation were calculated using analysis of variance techniques.

Main Results:

• Mean plasma ascorbic acid: 42±12 μmol/L; intra-individual variation: 26%.
• Mean plasma alpha-tocopherol: 31±3 μmol/L; intra-individual variation: 12%.
• Critical difference for significance: 72% for ascorbic acid, 34% for alpha-tocopherol.

Conclusions:

• Both ascorbic acid and alpha-tocopherol exhibit marked intra-individual variability.
• Individual reference values are more clinically useful than population-based data for antioxidants.
• Alpha-tocopherol requires a smaller change to be statistically significant compared to ascorbic acid.