Vitamin C Depletion has Links to Lower Fat Oxidation, But Not Weight Loss

Too little vitamin C in the blood stream has been found to correlate with increased body fat and waist measurements. ASU nutrition professor and researcher Carol Johnston, and nutrition graduate student Bonnie Beezhold, report that the amount of vitamin C in the blood stream is directly related to fat oxidation — the body's ability to use fat as a fuel source — during both exercise and at rest.

Before beginning a strictly controlled, calorie reduced diet, 20 obese men and women were randomized by gender and body weight into either a vitamin C group that took a 500 mg vitamin C capsule daily or a control group that took a placebo. Neither participants nor researchers knew who was receiving which capsule until the study was over.

All participants consumed the same experimental diet that the researchers adjusted individually to promote slow weight loss, about two pounds per week. The low-fat diet contained 67 percent of the USRDA (recommended daily allowance) for vitamin C, about 40 mg daily.

At baseline, participants with the lowest concentrations of vitamin C in their blood had the highest body fat mass and tended not to oxidize fat well, compared to their less obese counterparts.

After four weeks of diet adherence, blood vitamin C concentrations increased 30 percent in those taking vitamins and fell 27 percent in the control group whose only vitamin C intake was the 40 mg contained in the calorie reduced diet.

"We found that as vitamin C blood concentrations fell, so did the participants' ability to oxidize fat (an 11 percent reduction)," says Johnston.

The experimental diet worked for all participants. Although body fat mass decreased slightly more in the vitamin C group, approaching but not reaching statistical significance, both groups lost an average of nine pounds, indicating that vitamin C depletion did not appear to affect the ability to lose weight in the short term when dietary calories were strictly controlled. But because the study supported early findings by Professor Johnston's laboratory of a decrease in fat oxidation, the researchers will now examine whether poor vitamin C status is associated with a reduced ability to lose fat mass in individuals adopting a self-directed exercise program.

This research was supported by a grant from the General Mills, Bell Institute of Health and Nutrition.