The aim of the present study was to investigate the association between the MDS, its components and blood lipids, taking into account potential confounding factors such as age, BMI, PAL, energy intake and smoking. The results showed that there are only limited gender-specific relationships between total MDS or its components and blood lipids. A better blood lipid profile with an increasing MDS was hypothesized since the Mediterranean dietary pattern is characterized by a high consumption of vegetable food (including vegetables, pulses and whole cereals), a regular use of olive oil and low SFA. These factors are related with lower TC levels, which are considered as health protective [4, 30]. In our study, only weak associations with blood lipids were found in the non-adjusted and in the adjusted analysis. The results are more in accordance with the formulated hypothesis in men compared to women. The negative relation between MDS and LDL cholesterol in the adjusted analysis corroborate the findings of Pitsavos et al. , Panagiotakos et al.  and Fitó et al. , but in men only. Carter et al.  reported an increase in HDL cholesterol and a decrease in TC/HDL cholesterol with an increasing MDS. In the present study the same association was found, but only in men. Pitsavos et al.  and Carter et al.  found the same results in men and women. Panagiotakos et al.  adjusted for gender and Yang et al.  only included men. Different relations between the MDS and blood lipid profiles found for men compared to women can be explained by the fact that some physiologic and metabolic factors may induce other responses in women compared with men, such as menopausal status and the use of hormone replacement therapy . Genetic differences may also induce different responses in the blood lipid profile. There are some effects of estrogen that may predict benefits .
The weak relations found in our study are in line with the results from the Lyon Diet Heart study, in which was found that a Mediterranean diet does not qualitatively alter the reported relationships between the risk factors of CHD, such as blood lipids, and the recurrence rate of CHD . Moreover, the association between CHD and the dietary intake of polyunsaturated fatty acids (PUFA) and SFA was contested by the meta-analysis of Chowdhury et al. , concluding that there is no clear evidence for the present cardiovascular guidelines encouraging low consumption of SFA and high consumption of PUFA.
As a consequence, uncertainties remain about the cardio-protective mechanism of the Mediterranean diet. According to de Lorgeril et al. , other Mediterranean lifestyle factors such as the absence of stress and pollution, the economic situation and the presence of health systems and extensive welfare are postulated as possible explanations for the protective effect. However, also in non-Mediterranean populations health effects can be obtained by adherence to a Mediterranean diet . The reduction in CHD prevalence with comparable lipid and lipoprotein risk factors points to other important risk factor modifications influencing the development of CHD . Oxidative stress due to the antioxidant capacity of the diet, decreased inflammation and improved parameters of endothelial function are possible mechanisms linking the Mediterranean diet to reduced cardiovascular risk, whilst alpha-linolenic acid can contribute to the cardio-protective abilities [38, 39]. The role of PUFA, nitrite and polyphenols can also lower the cardiovascular recurrence rate . Another explanation for the lack of association between the Mediterranean dietary pattern and the blood lipid profile may be due to the influence of confounding factors. Adherence to a Mediterranean diet combined with other healthy lifestyle and genetic factors  may have an influence on the blood lipid profile. The latter factors are understudied in most reports, whilst they may help to explain the blurred relations between the MDS and blood lipids.
Comparing our results with those from other studies is complex, because little attention is given to confounders in most reports. Possible confounding factors are generally not clearly reported or controlled for in different ways, for example as a dichotomous variable, in more categories or in tertiles. Pitsavos et al.  and Yang et al.  reported the relation between the MDS and blood lipids in adjusted and non-adjusted analyses. Reductions in LDL cholesterol with an increasing MDS were found irrespective of various confounding factors . In the study of Yang et al.  only LDL cholesterol varied whether the analysis was adjusted or not. For HDL cholesterol and the ratio TC/HDL cholesterol, similar results were found for non-adjusted and adjusted analysis. Yang et al.  reported using an adjusted analysis lower LDL cholesterol with a higher mMDS as in the adjusted analysis of the present study and higher HDL cholesterol with a higher mMDS as in both the adjusted and non-adjusted analysis of the present study.
There are some limitations to the present study. The study has a cross-sectional design and can therefore not predict causality. Another limitation of the study is that dietary records and physical activity questionnaires are susceptible to reporting bias, and a healthy volunteer effect can be suspected. Adjustment for known influencing factors was done, but factors such as pollution, stress, economic factors and genetic factors were unknown. Literature indicates that blood lipids levels seem to be higher in postmenopausal women compared to premenopausal women . Information concerning menopausal status in women was not available. Hence, correction for this potential confounder was impossible. Equally, a review showed that blood lipids improved when people stopped smoking . In the present study smoking status was used as a possible confounding factor. Based on the questionnaire it was not possible to divide the participants into three smoking categories (former smoker, current smoker or non-smoker). Besides the high power and the integration of confounding factors, an important strength of this study is the debated research topic. The relationship between the MDS and blood lipids is insufficiently investigated whereas underlying mechanisms and confounding factors remain unclear. Hence, reports of non-significant results are likely to remain unpublished because of publication bias . Prospective research is needed to learn more about the associations between the MDS and blood lipids, potentially in combination with a cardiovascular endpoint.
Although the hypothesized relation between MDS, its components and blood lipids was not confirmed, previous studies have shown that adherence to the Mediterranean diet can be health protective . Literature shows that an increment in HDL cholesterol of 1 mg/dl is estimated to decrease the risk of CHD by 2% to 3% . According to earlier published papers, both the MDS and blood lipid profile seem to be separately associated with CHD. In the present study, there were only few associations between MDS, its components and blood lipids, even after adjustment for potential confounding factors.