Bleeding tendency and ascorbic acid requirements: systematic review and meta-analysis of clinical trials.

ABSTRACT

CONTEXT The World Health Organization set the recommended daily vitamin C intake, henceforth referred to as ascorbic acid (AA), on the basis of scurvy prevention. Double-blind AA depletion-repletion studies suggest that this recommended AA dose may be too low to prevent microvascular fragility. OBJECTIVES: (1) To conduct a systematic review and meta-analysis of controlled clinical trials on whether AA supplementation leads to a reduced gingival bleeding tendency, a manifestation of microvascular fragility; and (2) to relate AA plasma levels to retinal hemorrhaging, another manifestation of microvascular fragility. DATA SOURCES Data were reviewed from 15 trials conducted in 6 countries with 1140 predominantly healthy participants with measures of gingival bleeding tendency, and from the National Health and Nutrition Examination Survey (NHANES) III of 8210 US residents with measures of retinal hemorrhaging. RESULTS: In clinical trials, AA supplementation reduced gingival bleeding tendency when estimated baseline AA plasma levels were < 28 µmol/L (standardized mean difference [SMD], -0.83; 95%CI, -1.16 to -0.49; P < 0.002). Supplementation with AA did not unequivocally reduce gingival bleeding tendency when baseline estimated AA plasma levels were >48 µmol/L or unknown (respective standardized mean differences -0.23, 95%CI, -0.45 to -0.01, P < 0.05; and -0.56; 95%CI -1.19 to 0.06, P < 0.08). In NHANES III, prevalence of both retinal hemorrhaging and gingival bleeding tendency increased when AA plasma levels were within the range that protects against scurvy (11-28 µmol/L; respective prevalence ratios adjusted for age and sex 1.47; 95%CI 1.22-1.77; and 1.64; 95%CI 1.32-2.03; P < 0.001 for both). CONCLUSION: Consistent evidence from controlled clinical trials indicates that setting human AA requirements based on scurvy prevention leads to AA plasma levels that may be too low to prevent an increased gingival bleeding tendency. Gingival bleeding tendency and retinal hemorrhaging coincide with low AA plasma levels and thus may be reflective of a systemic microvascular pathology that is reversible with an increased daily AA intake.