In the present study, we found a significantly associated between a high dietary TAC and reduced risk of hypertension - independent of other risk factors for hypertension including overweight, obesity, physical inactivity and dyslipidaemia- in pre/perimenopausal women; however, this association was not significant in postmenopausal women.
We found that women with the most intake antioxidant had significantly higher HDL-C, and lower LDL-C and T-C. Dyslipidaemia is one of the most important risk factors for hypertension (24). A study by Kashyap et al. has showed that blood lipid levels were higher in subjects with high blood pressure compared to subjects of with normal blood pressure (25). The plasma malonialdehyde (MDA) increases in subjects with hypertension, MDA is the end product of non-enzymatic degradation of polyunsaturated fatty acids (PUFA). Actually, higher levels of MDA in hypertensive individuals indicate an increase in lipid peroxidation, and an increase in the production of peroxides in the cell membrane leads to the production of free radicals. Free radicals also cause dyslipidaemia and increase uric acid and plasma homocysteine, that is why subjects with hypertension have dyslipidaemia (25). Therefore, a diet rich in antioxidants may have a double role in the prevention of hypertension.
According to the evidence, oxidative stress is caused by the overproduction of oxygen free radicals or a decrease in the concentration of antioxidants in the body (2). On the other hand, Hypertension is indirectly the result of an imbalance of antioxidants to inhibit free radicals (2, 26). Meta-analysis studies have shown that increased intake of fruits, vegetables and vitamins is associated with a reduced risk of developing hypertension (18, 19). Our findings also show that the intake of legumes, nuts, tea & coffee, fruit juiced and omega 3, omega 3, vitamin B1, vitamin B2, vitamin B6 and vitamin D were significantly lower in women with hypertension. A just one study on French women has shown a significant association between dietary TAC and hypertension (9). Ahmad et al. (2017) have suggested that the antioxidant therapy to reduce oxidative stress is a promising strategy for prevention and treatment of cardiovascular events involving hypertension (28). However, In a clinical trial study, no association was found between antioxidant supplementation and a reduction in hypertension (27). On the other hand, it is important to note that many antihypertensive drugs currently used in clinical practice, including calcium channel blockers, and β-blockers, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers; in addition to reducing BP, adrenergics can also reduce the antioxidant effects and activity of several vascular matrix metalloproneinases (29). Similarly, in hypertensive rats have been shown that antihypertensive drugs such as osartan, nifedipine, metoprolol, nebivolol and nimodipine to reduce vascular oxidative stress and matrix metalloproneinases expression, and thus have an antioxidant effect (30, 31). Overall, these findings support the theory that hypertension can be treated with dietary / natural antioxidants. However, clinical trial studies are clearly needed to determine the responsibility of oxidative stress on hypertension and the possible therapy of high blood pressure with antioxidants.
The findings of this study showed, dietary TAC has a protective effect for hypertension in pre/perimenopausal women and no protective effect was observed in postmenopausal women. One of the reasons for this difference is that postmenopausal women are older and so other risk factors are stronger and the role of antioxidants is less. Therefore, following a diet rich in antioxidants from adolescence and young adults can have a preventive effect.
The strengths of this study include the following: large sample size, using of RaNCD prospective study data and using a valid questionnaire with 137 food items to calculate dietary TAC. This research is the first study in Iran on a large population of women of Kurdish ethnicity. One of the limitations of this study is its cross-sectional nature. There is a measurement error that we always encounter in collecting nutritional information. In addition, in the food frequency questionnaire used in this study, local foods were also included, therefore to prove the generalizability of the results, it is necessary to conduct more studies in different regions and with different dietary patterns.