A small study from Arizona State University this summer found that low levels of vitamin C in the blood were linked to decreased fat oxidation.1 (Fat oxidation involves the breakdown and burning of fat for energy.)
"Individuals with marginal vitamin C status oxidized 25% less fat per kg body weight during a 60-minute treadmill walk as compared to individuals with adequate vitamin C status."The researchers also found that participants with the lowest vitamin C status, and the lowest ability to burn fat for fuel, tired more easily during exercise. It led them to speculate:
"Vitamin C depletion may result in weight gain by two mechanisms: indirectly by fatigability and exercise intolerance, and directly by lipid [fat] accumulation."In keeping with the theme - at the start of the trial those with the lowest levels of vitamin C in their blood had the highest body fat mass.
Vitamin C assists in the manufacture in the liver of the molecule carnitine. Carnitine is necessary for fat oxidation - it alone can transport long chain fatty acids across a mitochondrial membrane to be "burned" or metabolized for energy.
We've known for a while that vitamin C is used to make carnitine, and that carnitine is used to metabolize fat. Why it's taken so long to investigate vitamin C's impact on fat directly sets my flab to burn.
Are Americans Getting Enough Vitamin C?
Up to 17% of Americans are vitamin C deficient.
Up to 23% of Americans are vitamin C depleted. (This was the study's "marginal status".)
Add those together and you get about 40% of Americans who are not getting at least adequate amounts of vitamin C.2
(I consulted data from the very large, trustworthy, comprehensive, and tax-dollar-supported NHANES III report. It reflects intake from 1988 to 1994. Intakes for vitamin C today may be higher - or lower.)
Right on Target: During recruitment for participants, this study screened 78 non-smoking men and women from a campus population (aged 18 to 38). About 40% of this group had marginal vitamin C status (from a blood test). The non-smoking criterion was important - smoking, even just breathing passive smoke, reduces blood levels of vitamin C.
How Much Vitamin C Does the Job?
The vitamin C-depleted participants in this study consumed a diet that provided about 40mg/day. They were the "marginal" consumers.
The RDA for vitamin C is 75mg for females, 90mg for males. Add 35mg if you smoke.
The vitamin C-repleted participants in this study consumed a diet that provided about 40mg/day, plus were given a 500mg/day supplement. In 4 weeks that supplement increased their vitamin C blood levels by 30% and resulted in raising fat oxidation 4-fold when compared to depleted subjects.
If you decide to supplement with vitamin C based on this study, that is, with 500mg/day, consider that intakes of more than about 200mg at a time don't appreciably affect blood levels. (What doesn't get absorbed goes on to the colon for fermentation by bacteria. Yum, yum, eat 'em up.) I'd recommend buying a low-dose supplement and taking it 2 or 3 times/day.
2 Vitamin C Deficiency and Depletion in the United States: The Third National Health and Nutrition Examination Survey, 1988 to 1994
Photo: Homegrown. An average Clementine has about 36mg vitamin C, a medium orange (2.5 inches in diameter) has about 60mg.