Positive Health Online

Abstract

BEHNDIG and COLLEAGUES,  Department of Respiratory Medicine and Allergy, University Hospital, Umea, Sweden conducted a double-blind study with healthy individuals with low plasma ascorbate levels to determine whether human respiratory tract lining fluid (RTLF) ascorbate levels could be augmented through vitamin C supplementation.

Background

Low molecular weight antioxidants within human respiratory tract lining fluids (RTLFs) have been proposed to confer protection against the damaging action of inhaled oxidant gases. There is therefore considerable interest in augmenting the concentrations of these moieties at the air-lung interface to protect against injury to the airway epithelium, the induction of inflammation, and declines in lung function.

Methodology

To determine whether RTLF ascorbate concentrations could be augmented through vitamin C supplementation, 24 healthy subjects with low plasma ascorbate (< 50 microM) were recruited into a double-blinded study. Subjects were divided into two groups, one receiving 60 mg/day of vitamin C for 14 days, the other placebo. On days 8 and 15 of this protocol, plasma, urine, and nasal lavage were obtained for ascorbate determination. After a 7-14-day non-intervention period, subjects previously on placebo received supplements containing 125 mg ascorbate, whilst the group previously on supplements received the placebo compound. This 'switching' protocol was repeated three more times utilizing 250, 500, and 1000 mg/day ascorbate dosage regimens.

Results

Plasma ascorbate increased incrementally with vitamin C dose, as did its urinary excretion. Despite this, nasal lavage concentrations remained unaltered 24 h after the final supplement at all doses. Closer examination of this issue demonstrated that nasal lavage ascorbate concentrations increased acutely after ingestion of a high dose (1000 mg) supplement, peaking at 2-4 h (p < 0.05) before returning to baseline concentrations 24 h post-supplement. In the absence of a quantitative association between plasma and lavage ascorbate concentrations, the authors contend that this response does not simply reflect ascorbate transudation from the plasma and interstitial space into the lavage medium.

Conclusion

The authors conclude that RTLF ascorbate can be augmented, albeit transiently, by oral vitamin C supplementation, with the transient nature of this response likely reflecting oxidative losses within the RTLF or its sequestration into airway cells.

References

Behndig AF, Blomberg A, Helleday R, Kelly FJ and Mudway IS. Augmentation of respiratory tract lining fluid ascorbate concentrations through supplementation with vitamin C. Inhalation Toxicology. 21 (3): 250-8. Feb 2009.