1 Department of Physical Education, National Public Health Management Center. Tabriz University of Medical Sciences (IRI, Tabriz).
2 Karayev Institute of Physiology, Azerbaijan National Academy of Sciences (Baku)

Эта статья опубликована сборнике научных трудов "Проблемы и перспективы современной науки" с материалами Четвертой Международной Телеконференции "Фундаментальные науки и практика" - Том 3 - №1. - Томск - 2011.

 

-- Summary

The hyperglycemia and lipid profile abnormalities of type 2 diabetes mellitus (T2DM) can be improved by aerobic (AE) or resistance (RT) exercise. The relationship between A1C and lipid profile changes was investigated in a randomized-controlled study. Sixty patients with type 2 diabetes mellitus were randomly entered in AE, RT and control groups (20 subjects in each group). AE and RT, groups performed training sessions 3 times per week for one year. A1C and lipid profile (TC, LDL-c, HDL-c, and TGs) were measured before and after the intervention. At the end of intervention, AE and RT resulted in significant differences in A1C level (-1.33±1.08 and -0.55±0.47 respectively, P<0.001). All sub-fractions of lipid did not show the same alterations. TGs of AE and RT groups had significant differences compared to control group, whereas only AE group had statistically significant changes in comparison to its previous value. The elevation of HDL-c only achieved significance in RT group, whereas each of the groups did not show any significant alteration for LDL-c and TC parameters. The present study indicates that improvement of A1C values is not necessarily associated with apparent modification in all of lipid parameters as cardiovascular risk factors.

-- Introduction

The prevalence of diabetes has an increasing rate and is associated with personal and social costs. Type 2 diabetes mellitus (T2DM) account for 90 – 95% of all diabetes cases. The long – term complications associated with type 2 diabetes are both microvascular and macrovascular in nature and include the retinopathy, peripheral, and autonomic neuropathy, peripheral vascular disease, atherosclerotic cardiovascular events, cerebrovascular disease, hypertension, and susceptibility to infections and periodontal disease [2, 1]. T2DM is associated with a 2 to 4 – fold high risk of cardiovascular disease, which can be partly attributed to dyslipidemia. A decrease in TGs may favorably impact on cardiovascular risk. The goal of treatment in T2DM is to achieve and maintain near – normal blood glucose levels in order to prevent or delay its macro – and microvascular complications [21, 2].
Exercise along with dietary regimen represents an effective intervention for people with T2DM and shows a significant challenge to glycemic control and prevent or delay of life – treating complication such as heart disease. Exercise modifies lipid abnormalities and hypertension [4, 20]. Cardiovascular disease in patients with diabetes is clearly associated with the degree of hyperglycemia (as measured clinically with the use of glycated hemoglobin or A1C). An increase in physical activity has beneficial effects on metabolic control in T2DM patients [18]. The present study aimed to answer the question that: Dose the achieving to optimal levels of A1C by regular exercise reduces the rate of cardiovascular risk factors as measured by parameters such as lipid profile? Whether there is a relationship between changes of A1C and lipid profile or not? In addition, we compare the effects of two forms of exercise, aerobic, and resistance training on the changes of glycemic control or lipid profile parameters. Based on evidence, the American Diabetes Association (ADA) recommends that individuals with T2DM perform at least 150 min of moderate intensity aerobic exercise and/or at least 90 min of vigorous aerobic exercise per week. Since 2006, the ADA recognizes that in the absence of contraindications, these patients should be encouraged to perform resistance exercise 3 times a week [14].

-- Methods and Materials

The participants of this one-year randomized – controlled trial were T2DM patients who were recruited through clinics of Tabriz University of Medical Sciences. After baseline evaluation and a 2 – week run in phase period, a sample of 60 participants with 20 subjects in each group were randomly divided in aerobic exercise (AE), resistance training (RT), and control groups.
For inclusion purpose, subjects were screened for known duration of diabetes for at least one year, have only oral antidiabetic medicine, previous sedentary lifestyle, and values of A1C<11.
Exclusion criteria were insulin therapy, BMI 43, age over 70 years, possible previous cerebrovascular or cardiovascular disease, and severe microvascular events or arthritis.
Subjects were informed about the study design. All participations were recommended to continue their current drugs and diets. Also, their physicians were recommended to inform us the need for alterations in therapeutic regimen of patients. Control patients were also recommended to maintain their sedentary lifestyle. This program was conducted based on ACSM’s (American College of Sport Medicine) guidelines.
Baseline biochemical tests including glycosylated hemoglobin (A1C), total cholesterol (TC), high density lipoprotein-cholesterol (HDL-c), low density lipoprotein-cholesterol (LDL-c), and triglycerides (TGs) were taken both before and after the intervention. Physicians also repeated these tests on 3-monthly visits.

-- Exercise training protocol

Subjects of aerobic exercise (AE) and resistance training (RT) groups performed exercise program 3 times per week for one year. Training programs of two groups progressed gradually in duration and intensity. The protocol consisted 10 – 15 min of warm – up as well as same duration of relaxation movements to cool down. The AE was performed by using treadmill, eleptical, and static bicycle ergometers that was gradually increased from 20 to 60 minutes at 60-70% of maximum heart rate. RT involved with the weight machines and included 8-10 various trainings, 2-3 sets of each training repeating 8-10 times. These programs were done under the supervision of specialist trainers. Thus, no severe accident was not observed in two groups. After consideration of the attendance in more than 80% of sessions during one year and dropout cases, finally 45 patients (15 in each group) were entered statistical analysis. The mean age of participants was 50.4±8.1 years.
Statistical analysis were performed using SPSS (version 16.0). If ANOVA showed a significant difference, Tukey post hoc comparison was used to identify mean differences the changes between groups. The results are shown as mean ±SD with p value less than 0.05 as meaningful values.

 

--Results

The baseline characteristics of three groups are shown in Table 1

 

 

AE and RT groups showed significant reduction in A1C levels (P<0.001). The differences of AE and RT groups were -1.33±1.08 and -0.55±0.47 respectively. However, the participants of control group experienced an increase in A1C value (+0.20±0.66).
Lipid profile showed another pattern for various parameters. Total cholesterol (TC) and LDL-c had not significant charges in exercise groups or control group, whereas HDL-c level increased significantly in RT group (+4.67±5.19). Triglycerides (TG) levels reduced significantly in AE group (-58.87±65.12).
According to these data both the AE and RT groups differ from control group in A1C variable and two training groups differ from each other (P<0.05). Furthermore, both of them differ from control group in TGs variable (P<0.05), whereas there is no difference between two training groups in changes of this parameter.

The differences of A1C and lipids are shown in Table 2

 

Regular physical activity is recommended for patients with T2DM as a therapy cornerstone. Two of the major goals of diabetes therapy are to reduce hyperglycemia and cardiovascular events [5, 8]. AE has beneficial effects on glucose control as well as its abilities to retard the progression of other comorbidities such as cardiovascular disease. On the other hand, the glucose-lowering effects of RT have also been documented. RT has additional benefits such as the capacity to counteract sarcopenia, which is common in older people with T2DM [4, 12].
Increased aerobic power of T2DM people is related to a less atherogenic profile, which may lessen the accelerated rate of atherosclerosis and related mortality rate [2]. A1C is the gold standard for monitoring glycemic control and serves as an indicator for diabetic related disease. Meta – analysis of clinical trials shows that every 1% reduction in A1C lowers the major cardiovascular events by 15% to 20%. Establishing glucose control at or below 7.0% reduce the long term complications by up to 76%. However, the relationship of A1C with cardiovascular disease in these patients is less clear than microvascular disease [15, 16, 20].
Even before glucose concentrations reach the diagnostic threshold for diabetes, 25% of newly diagnosed patients may already have appreciable cardiovascular disease. Most diabetic patients die from macrovascular complications than microvascular events [17].
In the present study both the AE and RT induced statistically significant reduction in A1C values compared control group, whereas the difference in AT group was less than the half of AE group. This finding is in line with finding of Sigal et al. [16]. In DARE trial who reported greater reductions of A1C for AE group compared with RT group. They demonstrated that either AE or RT alone improves glycemic control. However, the difference of two types of exercise in A1C value was approximately equal. (-0.51 for AE and -0.38 for RT), but their effects on plasma lipid levels were likewise modest. The changes of lipid values (TC, TGs, LDL-c, and HDL-c) in trial of Sigal et al. did not statistically significantly differ among groups. That is, in their study the changes of A1C value among AE, RT and even AE+RT group with additive improvement did not show a parallel alteration with the changes of lipid profile. They stated that to achieve greater changes in these variables higher volume, or intensities of exercise must be necessary.
In our study the pattern of TGs changes is in order of A1C changes and AE can induce more improvement compared with RT and even subjects in control group have an increase in their TGs value at the end of program (171.27±78.5 to 220.93±97.9).
Reports on effects of RT on glycemic control in patients with T2DM have been controversial [7]. It seems that intensity of training or length of study may be attributable factors.
Our result do not confirm the findings of Cauza et al. who reported that the strength training (or RT) was more effective than endurance training (or AE) in improving of glycemic control as well as improved lipid profile. They observed a significant decline in A1C only in the RT group, whereas all of lipid parameters altered optimally. However, glycemic control had a positive correlation with the lipid profile. They concluded that improved lipid profile must be largely due to the changes in body composition as a result of RT [7].
In the study of Arora et al. A1C values were significantly reduced in RT and AE groups, but in contrast to our study total cholesterol (TC) concentrations were also significantly decreased in two RT and AE groups. Both exercise groups showed no significant change in HDL-c (TC) [3].
Castenada et al. compared the effects of high-intensity progressive RT with a nonexercise patients. They reported a significant reduction of A1C in RT group (8.7 to 7.6%), but no differences were observed in cardiovascular risk factors such as HDL-c, LDL-c and total cholesterol (TC) levels [6].
In contrast to this finding Honkola et al. reported improved lipid profile (as decreased LDL-c, TGs, TC and increased HDL-c levels) with no significant reduction in A1c after 5 months of progressive circuit RT [10].
Eriksson et al, evaluated the effects of RT for 3 months. They observed meaningful decrease in A1C value without changes in HDL-c, LDL-c, and TGs values. Furthermore, results of Dunston et al. after 6 months RT plus weight losing program in T2DM patients is in line with finding of Eriksson et al. [9, 10].
Their results have similarity to our results in RT group except HDL-c parameter, which had significant increase [10]. On the other hand, these two trials don’t demonstrate any positive correlation between A1C and lipid profile improvement. Another study by Gold-fiebert indicates that an exercise program as walking plus nutrition intervention resulted in a significant change in A1C percent point and non-significant changes in serum lipids [11].
A meta-analysis conducted by Kelly and Kelly in order to examine the effects of 8 weeks or more of AE on lipids and lipoproteins in type 2 diabetic adults suggest that AE lowers LDL-c as well as A1C levels. This finding confirms the issue that the increased risk for cardiovascular disease in individuals with less than optimal lipid levels and uncontrolled glycemia are parallel with each other [13].
The results of AE group in our study confirm the findings of Alam et al, that a supervised AE in T2DM patients resulted in a lowered concentrations of TGs along a significant decrease in percent hemoglobin A1C.They hypothesized that a decrease in VLDL apoB secretion rate may be due to an increase in hepatic insulin sensitivity and the decrease in TGs with regular exercise may be due to a decrease in VLDL apoB secretion rate. Their study suggests that a decrease in TGs may favorably impact on cardiovascular position [1].
Another report previously published by Walker et al, indicated that regular walking for 12 weeks had positive effects on glycemic and cardiovascular control of women with T2DM compared with normoglycemic women. In diabetic women LDL-c and total cholesterol (TC) concentrations fell significantly, but there was no change in HDL-c value [19].
The association of between glycemic targets and cardiovascular disease (without considering the effect of exercise) was studied in two important trials (ACCORD and ADVANCE trials). Both trials evaluated an intensive treatment for blood-glucose-control, rather than a specific therapeutic regimen. Corresponding result showed that targeting A1C levels below accepted standards in high risk patients did not have a beneficial effect on cardiovascular disease [8].

 

-- Conclusion

An exercise program as a lifestyle modification is associated with the reduction of A1C values that reflects better control of glycemia. This program is not always successful to improve all of lipid sub-fractions as a part of cardiovascular risk factors in T2DM patients.
Our study suggest that at least in regarding to TGs levels, the favorable effects of AE or RT compared to control group are combined with optimal decreases of A1C percentage by AE or RT which presents a direct relationship between improvement of blood glucose control and sustained cardiovascular risks. However, the alterations of lipid profile sub-fractions don’t necessarily follow the same pattern of A1Cchanges. A clear relationship of glycemic control with cardiovascular position need to be interpreted along with other measurements such as blood pressure, body mass index (BMI), body fat percentage as well as other effectors such as intensity, volume or duration of exercise training program.
However, whether achieving glycemic targets below 7% through lifestyle changes such as increased physical activity will be beneficial to lowering risk. Factors of cardiovascular disease, remains unanswered.

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