Vitamin C is essential for the synthesis of carnitine, a compound required for fatty acid oxidation – the utilization of fatty acids as energy – commonly referred to as “fat burning.” Carnitine deficiency is associated with fatigue and poor exercise tolerance. Findings from a new study suggest that high dose vitamin C improves fatty acid oxidation.

The two-part clinical study involved 22 men and women between the ages of 18 and 38 years. Fifteen of the participants had marginal vitamin C blood levels (less than 34 micromoles per liter) and seven had adequate vitamin C blood levels (greater than 34 micromoles per liter).

In the first part of the study, all of the participants completed a 60-minute treadmill walk at 50 percent of their VO2 max. Fat utilization during the treadmill walk was 25 percent lower among participants with marginal vitamin C status, suggesting that vitamin C status affects fuel utilization during exercise.

In the second part of the study, the participants' vitamin C levels were depleted over a period of four weeks. Then they took either 500 milligrams of vitamin C or a placebo every day for four additional weeks. At the end of the eight-week period, the average blood vitamin C levels in the supplemented group were 41.7 micromoles per liter, but average levels among the depleted group were 9.7 micromoles per liter. Fatty acid utilization in the supplemented group was approximately four times greater than the vitamin C depleted group. Poor fatty acid oxidation during exercise was related to higher levels of fatigue.

These findings suggest that low vitamin C status is associated with poor fatty acid oxidation during exercise and may explain why some people are unsuccessful when trying to lose weight.

• Link to full study.