4. Discussion
Large number of studies has repeatedly demonstrated that consumption of the DASH diet could decrease BP in hypertensives[10,11],but it has been less commonly used in hypertensive patients with T2D. In the study by Azadbakht et al.[13], after 8 weeks of DASH diet intervention among patients with T2D, the intervention group had a significant BP reduction compared with the control group. Paula et al.[12]also had a similar conclusion, but in the study of Hashemi et al.[17], there was no significant difference in the reduction of BP between the DASH diet and the control diet. To the best of our knowledge, this is the first study evaluating the effects of DASH eating pattern on BP among Chinese patients with hypertension and T2D.
We modified the original DASH diet according to the dietary habits of Chinese people, and formed CM-DASH diet. Participants had high compliance during the intervention, and no one dropped out because of diet,which indicated that CM-DASH diet was meets the dietary preferences of Chinese people.Our study revealed that hypertensive patients with T2D who followed a CM-DASH diet during an 8-week period had a major reduction in SBP and DBP. From baseline to 8 weeks later, the mean SBP had decreased by 14.32 mmHg in intervention group,10.98mmHg in control group and ,the mean DBP had decreased by 6.32 mmHg in intervention group,5.24 in control group.The largest reduction in BP was observed in SBP at the end of week 4, approximately 18 mmHg in the intervention group, 12mmHg in the control group.
Sodium reduction was considered to be a factor underlying the hypotensive effect observed in this study. The baseline mean salt consumption of participants in this study was 8.94g per day, but with the CM-DASH diet, the mean salt intake of participants was reduced by approximately 4g per day. As the golden criteria to determine the intake of sodium, 24-hour urine electrolyte electrolytes has been widely used in scientific research[18].Our results shows that after the intervention of CM-DASH diet, the 24-hour urine Na+ of the intervention group and the control group both decreased significantly, which indicated that CM-DASH diet had a marked effect on reducing the sodium intake of the participants. Studies have shown that high dietary sodium intake can lead to high BP by inhibiting the activity of Na + - K+ - ATPase pumps in cell membrane[19], damaging vascular endothelial function[20]and activating RAAS (Renin-Angiotension-Aldosterone System)[21]. There is substantial evidence that reducing sodium intake lowers BP in persons with hypertension. We also found similar hypotensive effects in patients with hypertension and diabetes.
Contrary to the effect of sodium on BP, potassium can lower BP by stimulating Na + - K + - ATPase pumps and the opening of potassium channels in vascular smooth muscle cells and adverse nerve receptors[22].The DASH diet also recommends reducing dietary sodium and consuming more potassium-rich fruits and vegetables[9], but it is hard to achieve the desired effect by supplementing potassium with food. Studies have shown that increasing potassium intake by consuming low sodium salt is an effective and economical way[23]. We used low-sodium salt with a sodium chloride content of 52% and a potassium chloride content of 31% in the intervention group, while the control group used common salt with a sodium chloride content of >99%. Our results showed that there were significant changes in 24-hour urinary K+and Na+ / K+ ratio in the intervention group, but not in the control group. Although there is no significant difference in BP drop between the intervention group and the control group, we observed that the decrease of SBP in the intervention group appeared earlier and more significantly than that in the control group. In view of previous studies[24,25] suggest that the high level of potassium in the DASH diet is important for its hypotensive effects,we still consider that the application of low-sodium salt in the DASH diet may have more beneficial effects on BP reduction in hypertensive patients with T2DM, and a significant difference may be found by increasing the intervention time and expanding the sample size.
It was considered that the high potassium content of the low-sodium salt could result in hyperkalemia and safety monitoring was conducted. During the study period,
no serious adverse events occurred, and the safety of the participants was monitored and confirmed throughout the study period. Serum test results showed that there was a slight increase in potassium during the intervention period, but it was still within the normal range. In addition, there is no significant difference in the changes of AST, ALT, UA, Urea. However, urine UACR and serum creatinine showed a significant decrease compared with baseline in two groups , which may be related to the reduced sodium intake in the CM-DASH diet. Studies have reported that excessive salt intake is associated not only with high BP but also target organ damage[26].There is an association between high salt intake and UACR independent of BP, and oxidative stress is a modifying factor between them[27].The research of Feng J. He et al. showed that with the salt reduction, the urine albumin and UACR also decreased significantly[28]. In view of these results, we believe that short-term CM-DASH diet and sodium reduction feeding trials may have beneficial effects on the improvement of renal function.
Most evidence for the DASH diet comes from short-term feeding studies[10,29] or dietary behavioral intervention studies[30],but both methods were used in this study. Interestingly, although the dietary and salt requirements for participants during the dietary behavior intervention were the same as those during the feeding trial, we still observed a small increase in BP in phase 3, which was also confirmed by the changes in urine Na+ and K+ in 24 hours. Cooking meals that meet dash nutritional requirements at home is affected by many interference factors, which makes it difficult for participants to strictly comply with our recommendations. On the other hand, CM-DASH diet menu contains coarse grains, low-fat milk and nuts, which is difficult for Chinese people to consume on a regular basis. It will take longer to change the eating habits of Chinese people that have lasted for thousands of years. In the future, we should strengthen health education on diet to change the dietary behavior of Chinese people with hypertension and T2D.
In conclusion, The results of the present study demonstrated that 52% low-sodium salt applied to the CM-DASH diet is an effective nutritional strategy for the control and management of BP in Chinese people with hypertension and T2D.