Lead researcher, Professor Carol Johnson, told NutraIngredients.com: "This is all important because about 30 per cent of Americans have poor vitamin C status as indicated by blood vitamin C concentrations."
Despite these deficiency statistics, the image of vitamin C supplements with consumers is strong. According to Frost and Sullivan, the US market generated $151.7m (€127.4m) in 2005. In Europe, revenue was calculated at $160.3m (€134.6m) for 2005, and is expected to grow to $192.5m (€161.6m) by 2011.
Bonnie Beezhold and Professor Johnston from Arizona State University presented the results of a double-blind, placebo-controlled trial of 20 obese men and women on a low-fat diet. One group's diet was supplemented with a 500 mg vitamin C capsule, while the other group received an identical-looking placebo.
The diet was formulated to provide 67 percent of the US RDA (recommended daily allowance) for vitamin C.
At the beginning of the trial, volunteers with the lowest serum concentrations of vitamin C were found to have the highest body fat mass.
After four weeks, the supplemented group had increased serum concentrations of vitamin C of 30 per cent, while the control (placebo) group's blood levels decreased by 27 per cent.
As vitamin C blood concentrations fell, so did the participants' ability to oxidize fat (an 11 per cent reduction). Interestingly, both groups lost the same amount of weight (4.1 kg, 9 lbs). While body fat mass decreased more in the vitamin C supplemented group, the difference was not statistically significant.
The study supported earier findings by Professor Johnston of a decrease in fat oxidation, and the researchers are now studying whether the impact of vitamin C status is associated with a gradual gain in body fat in non-dieting individuals.
The mechanism behind the vitamin C effect is linked to its essential role in the synthesis of carnitine, an amino acid responsible for the transport of fatty acids.
"Carnitine is important for fat oxidation - and the reduced ablility to oxidize fat creates fatigue and possibly retention of body fat," explained Johnston.
"Since fatigue is the earliest sign of a vitamin C deficiency, I am particularly interested in documenting this fatigue and whether it has a significant impact in metabolism," she said.
The recommended daily intake of the vitamin in Europe is 60 mg. In the US, men are recommended to consume 90 mg per day, and women 75 mg per day.