In the present study we investigated the plasma levels and nutrient intake of antioxidants that are abundant in the traditional Mediterranean diet, i.e. carotenoids, vitamin C, vitamin E and selenium . After the intervention the consumption of several antioxidant-rich foods increased in the MD group, and as expected this group had a higher intake of most antioxidants compared to the CD group.
More surprising were the results for plasma antioxidants. Although the consumption of antioxidant-rich foods increased, the concentrations of plasma antioxidants were relatively constant throughout the study period. From baseline to the end of the study the plasma levels of α-tocopherol and γ-tocopherol even decreased to significantly lower concentrations in the MD group. Since tocopherols circulate in the blood with the lipoproteins, the plasma levels are often influenced by the blood lipid concentration. During the course of this study, the total cholesterol decreased significantly in the MD group (results presented elsewhere)  and it is possible that this change caused the decreased levels of plasma tocopherols as well. For this reason we expressed the tocopherol levels as the ratio of tocopherol:(total cholesterol+triglycerides) as proposed by Turnham et al . When the concentration of cholesterol and triglycerides was adjusted for, the changes in plasma α-tocopherol did not reach statistical significance. Usually, the concentrations of tocopherols are expressed as tocopherol:total cholesterol or tocopherol:(total cholesterol+triglycerides), but since γ-tocopherol only correlated to triglycerides we also calculated the γ-tocopherol:triglycerides ratio. When γ-tocopherol was presented in relation to triglycerides this concentration was also unchanged.
Nevertheless, although the reported intake of vitamin E was higher in the MD group, the lipid adjusted plasma levels did not increase. One reason for this could be a decreased intake of fat, since the bio-availability of vitamin E is affected by the presence of fat. For the same reason the fat intake could also have affected the levels of β-carotene. According to the diet history interviews the MD group had a significantly lower intake of total fat compared to the CD group (p = 0.005) (data not presented). However, the relation between the intake of fat and vitamin E in each meal must be investigated to clarify this. The intake of fat and biochemical markers of fat intake will be presented elsewhere.
The levels of tocopherols in the MD group may also have been affected by the increased intake of fish or other foods rich in polyunsaturated fatty acids (PUFA). These fatty acids are easily oxidized and may therefore increase the expenditure of vitamin E. Tulleken et al , compared two groups of RA patients receiving either supplementation with fish oil (rich in ω-3 PUFA) plus 12.9 mg α-tocopherol or coconut oil plus 10.3 mg of α-tocopherol daily. Although the coconut oil-treated group received slightly less α-tocopherol, by the end of the study measures of vitamin E status were significantly higher in this group compared to the fish oil-treated group.
The influence of antioxidant-rich foods on the plasma concentration of antioxidants has been investigated in healthy subjects. Zino et al , showed that an increased intake of fruit and vegetables resulted in a raised plasma concentration of vitamin C, α-carotene and β-carotene. Interestingly, these changes were seen within the first two weeks of intervention, indicating that the plasma antioxidants in question respond quite fast to changes in dietary intake of antioxidants. In contrast, the levels of tocopherols may be more difficult to elevate by means of increasing the intake of vitamin E-rich foods .
In healthy individuals the plasma levels of antioxidants may be affected by many factors other than the nutrient intake, such as the degree of absorption, intake of other nutrients, homeostatic regulation etc. How the plasma antioxidants of RA patients are influenced by intervention with an antioxidant-rich diet has, to our knowledge, not been studied before. A possible explanation for the lack of correlation between dietary intake and plasma antioxidants, in the present investigation, is that the plasma levels of nutrients are mainly influenced by the inflammatory process, and to a lesser extent by the dietary intake. Several authors have reported depressed antioxidant levels in the plasma or serum of RA patients [30–36]. In addition, Honkanen et al  showed that in 50 RA patients, six parameters of disease activity explained 66% of the variation in serum zinc. They also reported that the low level of serum selenium found in RA patients was associated with joint score. We found that plasma retinol, ascorbic acid and uric acid were inversely related to indices of disease activity. In contrast to our results, in one study the level of serum vitamin A was shown not to be associated with blood parameters of inflammation or the joint score . Only disease activity assessed by the physician was related to the level of vitamin A. However, in the NHANES III study, serum retinol was found to be lower in subjects with elevated CRP concentrations .
Others have suggested that the low plasma/serum levels of antioxidants seen in RA patients are a result of an inadequate dietary intake. A number of authors have documented poor intakes of antioxidants among RA patients [34, 39–41], but all studies are not in agreement . Furthermore, in all of the studies where the nutrient intake was reported to be deficient, the energy intake was also rather low. Thus, it is not unlikely that the subjects have underreported their dietary intake. In the present study we have primarily related the dietary intake to the AR according to the NNR. When under-reporters were excluded (one MD and two CD subjects) all the subjects reached the AR for vitamin A and C. However, with regard to the selenium intake, 27% (4/15) of the CD subjects did not reach the AR for selenium. For vitamin E there is no specified AR, but in comparison with the recommended intake (RI) all of the MD subjects and 60% (9/15) of the CD subjects (excluding under-reporters) reached the RI, which for most people is considerably higher than the requirement. Hence, the result of this study does not point towards an inadequate nutrient intake, perhaps with the exception of selenium. However, our subjects had volunteered to participate in a dietary intervention study and may not have been representative for Swedish RA patients in general. For instance, they might have had a greater interest in nutrition, and perhaps their dietary intake was, for this reason, better than the intake of other RA patients.
Since antioxidant-rich foods, such as fruit and vegetables, are in general regarded as healthy, it is possible that the subjects have over-reported their intake of these food items and consequently the nutrient intake would be overestimated as well. If this was the case it could explain the lack of correlation between nutrient intake and the plasma levels of the corresponding nutrient, at least if, for instance, subjects with a low nutrient intake over-report to a greater extent.
Even if the reported intake of food items and nutrients was correct, it may not have been sufficient to substantially raise the plasma levels. In the study on healthy subjects by Zino et al , an average extra intake of 700 g of fruit and vegetables per day resulted in raised levels of plasma antioxidants (vitamin C, α- and β-carotene). Regarding vitamin E, McGavin et al showed that an increased intake of vitamin E from, on average, 10 mg/day to 22 mg/day only resulted in a small increase in plasma α-tocopherol in healthy subjects . For patients with RA the required amount could be even higher due to the impact of the disease.
In the present study, we have mainly focused on well-known antioxidant nutrients. However, fruit, vegetables, olive oil and tea also contain phytochemicals, such as phenolic compounds, which in recent years have attracted increased interest [2, 3, 13]. Apart from functioning as antioxidants these compounds have been attributed anti-inflammatory, antibiotic, and anti-carcinogenic properties . In a recent study by Halvorsen et al, the total antioxidant capacity of dietary plants was measured by the FRAP assay . They found that the antioxidants vitamin C, α-tochopherol, α-carotene, β-carotene, lutein, zeaxanthin and lycopene only contributed to <25% of the FRAP values of most dietary plants. Their results suggest that other antioxidants may be of considerable importance for the total antioxidative capacity. However, at this point knowledge about the bio-availability and the in vivo activity of the different phenolic compounds is still insufficient.