*2.1.1 Smoking status and obesity*

Smokers and obese people often need higher RDA (at least 35 mg/day more than that needed by non-smokers and average weight individuals) to maintain an optimal health [5, 7]. This is due to the low plasma concentrations of vitamin C usually seen among these groups of people. For example, a study by Langlois et al. [9] revealed that 29.2% of smokers compared to 9% of non-smokers and 17% of obese and 14% of overweight individuals compared to the 5.5% of the general US population that do not take vitamin C supplement had deficient levels (>28 Umol/L).

The prevalence of vitamin C deficiency can be as high as 15% in the general population [10], but it doubled among smokers [11]. Oxidative stress and increased vitamin C turnover associated with smoking are responsible for the low vitamin C status among smokers [12, 13], but supplementation had been shown to counter such effects [14, 15].

Several studies in a review by Carr and Lykkesfeldt [7] linked a low vitamin C status with higher BMI. This is because the response to vitamin C is smaller among those with higher body weights [16]. The plasma vitamin C concentration as well as the RDA depend on the body weight of the individual largely [17].
