Vitamin C, or ascorbic acid is one of the most popular and widely recognized dietary supplements primarily because of its role in boosting the immune system. lts popularity began in the mid-70s, when Linus Pauling published his groundbreaking book Vitamin C and the Common Cold 39, and from that time sales of vitamin C supplements skyrocketed, and maintained unbroken popularity until today. 13, 21, 37

Many health benefits have been attributed to ascorbic acid 37 but not only can vitamin C help us feel better and stay healthy but it also has been found to support weight management. Nutritional studies have found an inverse relationship between vitamin C status and body weight, waist measurements, and waist-to-hip ratios. 5, 31, 33, 35

How does Vitamin C do this? The specific mechanisms may be as follows:

  • Vitamin C is essential for the production of carnitine, which has a crucial role in lipid oxidation.
  • Vitamin C may actually increase the inclination to exercise.
  • Vitamin C may also help to modulate the actions of several hormones that are involved in fat-loss and/or fat accumulation, including cortisol, and insulin.



Vitamin C is an essential cofactor for the biosynthesis of carnitine. The breakdown of fatty acids to produce energy mainly occurs in mitochondria – the “energy furnace” of the cells. The main function of carnitine is to transfer fatty acids to mitochondria for subsequent oxidation.

Clinical trials have shown that tissue carnitine levels are directly related to vitamin C supply. 29, 24, 30, 31, 32, 45 And since the oxidation of fatty is dependent on carnitine this may be one of the main mechanisms by which vitamin C affects fat oxidation. 22, 43

In a study, individuals with marginal vitamin C status oxidized 25% less fat per kilograms of body weight during a 60 minutes treadmill walk as compared to individuals with adequate vitamin C status!

Moreover, 500 mg per day of vitamin C supplementation among vitamin C depleted subjects increased fat energy expenditure during exercise 4-fold as compared to depleted control subjects. 31


(Johnston et al., 2006)



Deficiency of key nutrients may result in changes in mental state, and functioning. For example, depression, fatigue and irritability precede the physical symptoms of the vitamin C deficiency disease scurvy. 6, 7, 34 Clinical studies observed that vitamin C supplementation may be linked with decreased fatigue, reduction in the perception of exertion during physical activity, diminished aversion to exercise, and improved mood states. Hence, vitamin C may positively impact physical activity in the general population, and especially among the obese. 6, 7, 9, 10, 11, 32, 36



Insulin plays an important role in the physiology of weight regulation. 4, 8 Insulin resistance, a condition in which cells fail to react normally to the insulin, is a driving factor in the development of type 2 diabetes mellitus, and is associated with a number of health conditions including obesity, and especially central adiposity. It may also make harder to control appetite by disturbing the believed role of insulin as a neuropeptide, involved in satiety, and appetite regulation. 2, 12, 19, 20, 25, 47, 41, 42, 48

As obesity and diabetes reach epidemic levels in the developed countries, the role of insulin resistance is gaining much attention. The possible insulin-sensitizing properties of vitamin C has been found in several investigations. 16, 17, 18, 30, 46, 48

Data from the EPIC-Norfolk study found an inverse relationship between plasma vitamin C and plasma glycated hemoglobin (HbA1c), a reliable indicator of insulin resistance. 16, 44, 48

Studies suggest that chronic low-grade inflammation and oxidative stress play a role in the development of insulin resistance, while antioxidants such as vitamin C may play a protective role against the development of impaired insulin sensitivity and type 2 diabetes. 16, 44, 48



Cortisol is glucocorticoid hormone that is released by the adrenal glands in response to stress as part of the “fight-or-flight” mechanism. It is essential for survival, but chronic stress, and thus chronic exposure to elevated cortisol levels is associated with adiposity and the persistence of obesity over time. 1, 18, 27

Studies have shown that Vitamin C may play a role in the regulation of glucocorticoid release, especially in highly stress situations. 3, 18, 38, 40 In a study, supplementation with 1500 mg of vitamin C among ultramarathon runners resulted a significantly lower post-race serum cortisol compared to no supplementation, or even to supplementation with 500 mg. 40



Official recommendations for adults: 15, 26




Recommended Dietary Allowance (RDA)

set by the Institute of Medicine (US)

75 mg/day

90 mg/day

Average Requirement (AR) 

set by the European Food Safety Authority (EFSA)

80 mg/day

90 mg/day

Population Reference Intake (PRI) 

set by the European Food Safety Authority (EFSA)

95 mg/day

110 mg/day


Studies mentioned above found beneficial effects at higher level of vitamin C consumption, in the range of 200 to 3000 mg of vitamin C per day. 3, 6, 9, 10, 13, 23, 32, 40, 50

According to its safety health authorities and organizations established upper intake levels for nutrients to determining safety of dietary bioactive components.

Tolerable upper intake level (UL) is the maximum level of total chronic daily intake of a particular nutrient judged to be unlikely to pose a risk of adverse health effects.

Institute of Medicine (US) set a tolerable upper intake level of 2000 mg per day for vitamin C for adults. 26


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