Bioavailability of vitamin C from kiwifruit in non-smoking males: determination of ‘healthy’ and ‘optimal’ intakes

Abstract

Vitamin C is an essential nutrient in humans and must be obtained through the diet. The aim of this study was to determine vitamin C uptake in healthy volunteers after consuming kiwifruit (Actinidia chinensis var. Hort. 16A), and to determine the amount of fruit required to raise plasma vitamin C to ‘healthy’ (i.e. >50 µmol/l) and ‘optimal’ or saturating levels (i.e. >70 µmol/l). Leucocyte and urinary vitamin C levels were also determined. A total of fifteen male university students with below average levels of plasma vitamin C were selected for the study. Weekly fasting blood samples were obtained for a 4-week lead-in period and following supplementation with, sequentially, half, one, two and three Gold kiwifruit per d for 4–6 weeks each, followed by a final 4-week washout period. The results showed that addition of as little as half a kiwifruit per d resulted in a significant increase in plasma vitamin C. However, one kiwifruit per d was required to reach what is considered healthy levels. Increasing the dose of kiwifruit to two per d resulted in further increases in plasma vitamin C levels as well as increased urinary output of the vitamin, indicating that plasma levels were saturating at this dosage. Dividing the participants into high and low vitamin C groups based on their baseline plasma and leucocyte vitamin C levels demonstrated that it is critical to obtain a study population with low initial levels of the vitamin in order to ascertain a consistent effect of supplementation.

Mood improvement in young adult males following supplementation with gold kiwifruit, a high-vitamin C food

“…Participants were provided with kiwifruit each week and were asked to consume half or two kiwifruit/d. The vitamin C content of the kiwifruit as monitored by HPLC with electrochemical detection ( 22 ) was 116 ( sd 9) mg/100 g fruit ( n 5). The participants were asked not to consume the skin, and based on the actual amount of fruit ingested, the amount of vitamin C consumed was calculated to be about 53 mg per half kiwifruit or about 212 mg for two kiwifruit.…”

“…The participants recorded their daily food and beverage intake for 1 week both pre- and post-intervention as described previously ( 22 ) . The vitamins C and E and β-carotene content of the foods and beverages consumed by the participants were estimated using Diet Cruncher software (version 1·6; Way Down South Software) and the New Zealand FOOD files Food Composition Database (2006).…”

“…Hort16A) on the subjective mood of young adult males. We have previously shown that consumption of half a kiwifruit/d results in a significant increase in plasma vitamin C in individuals with low fruit and vegetable intakes, while two kiwifruit/d are required to saturate the plasma, as indicated by a significant increase in urinary vitamin C excretion at this dose ( 22 ) . Therefore, in the present study we compared the effect of a low-dose intervention (half a kiwifruit/d) and a high-dose intervention (two kiwifruit/d) on subjective mood in our participants.…”

New Reference Values for Vitamin C Intake

“…In subjects on a vitamin C-deficient diet, urinary excretion declines rapidly to undetectable values [34,45] . As mentioned before (see 'Body Pool and Losses'), urinary excretion rises with rising plasma ascorbate concentration or vitamin C intake, respectively [14,15,18,40] , with ascorbic acid excreted in urine even at low, not yet deficient, plasma ascorbate concentrations and there is an abrupt rise in excretion at plasma concentrations near saturation [10,36,37,41,42] . However, the measurement of urinary ascorbic acid is of limited value as a marker for vitamin C status.…”

“…At a vitamin C intake of 100 mg/day, about 25% of the vitamin C intake is excreted in the urine [14,26] . Excretion is strongly increased if the plasma concentration is between 45 and 60 μmol/l [10,36,37,41,42] ; therefore, proximate saturation of body pools is assumed at a concentration from about 50 μmol/l onwards [26] .…”