Correlation of blood Na + and K + levels with Body Mass Index in population of Garhwal region of Uttarakhand

1 Veer Chandra Singh Garhwali Government Medical Sciences and Research Institute, Srinagar, Uttarakhand, India . 2 Department of Pharmacology, Kannur Medical College, Anjarakandy, Kannur, Kerala, India. 3 Department of Community Medicine, Lala Lajpat Rai Memorial Medical College and S.V.B.P. Hospital, Meerut, India. 4 Department of Pharmacology, Kannur Medical College, Anjarakandy, Kannur, Kerala, India.


INTRODUCTION
High Body Mass Index (BMI) and disturbance in body Sodium (Na + ) and Potassium (K + ) levels are associated with high risk of adverse health effects.Obesity has been associated with an increased risk of coronary artery diseases, diabetes mellitus type 2, hyperlipidemia, hypertension and mortality.A metaanalysis observed an risk of about 10% in risk of coronary artery diseases with each 5 unit increase in BMI (Bogers et al., 2007).Hypertension is a major risk factor for CVD.It has been estimated that shift in the population blood pressure (BP) distribution to a 5mm Hg lower level may prevent 1/3 of strokes and 1/6 of coronary events (MacMohan et al., 1990).Na + and K + have been implicated in aetiology of hypertension.A high potassium diet has been claimed to give protection on high sodium diet, but in most population studies no such association has been found (Warren and Aberg, 1979).Meta analysis of randomised trial found BP falls of 3-5 mm Hg systolic and 1-2 mm Hg diastolic for Na + reduction in hypertensive's and reduction half this size in normotensives (He and MacGregor, 2002).For K + supplementation BP decreases of more than 3 mm Hg systolic and 2 mm Hg diastolic have been reported (Burgess et al., 1999).Intervention studies of effects of weight loss, low Na + intake and K + supplementation on BP have been inconsistent as to whether weight loss leads to lower BP with or without Na + intake (Dahil et al., 1958) and in at least one study with or without increased K + intake (Heyden et al., 1972).
It is unclear whether lower Na + intake decreases BP equally in overweight and non overweight individuals (Cooper et al., 1984), also combined effect of weight and Na + reduction on BP have not yet been quantified (Prineas, 1991).High sodium intake and unawareness about BMI as a factor for various adverse health complication needs assessment, so that lifestyle changes can be advised to the community.This will ensure a reduction in morbidity and mortality due to these complications.So, the present study is undertaken to analyse the correlation between these factors.
There has been no known research related to blood Na + and K + levels and its correlation with BMI is conducted in Garhwal region.Considering the unbalanced dietary habits of people and change in their life style, there is a need to address these problems at primordial stage by giving information about good dietary habits and better life style for healthy living.
Effects of age, BMI and electrolytes (Na + and K + ) as risk factor for hypertension have been extensively studied before.However, the relationship between these parameters, within their physiological range and blood pressure remained mostly uncovered.Previous researches repeatedly demonstrated elevation of blood pressure with age in those above 40 year old (Smulyan et al., 1983), most likely due to vascular changes.Additional studies have proved the positive correlation between age and blood pressure among those less than 20 years (Gundogdu, 2008, Dores et al., 2010).Similarly the association between BMI and Blood Pressure was extensively investigated in children (Falkner et al., 2006, Gundogdu, 2008), nonetheless, comparable studies in middle age adults are very limited (Saely et al., 2009, Dores et al., 2010).
This study helps to evaluate the association of blood Na + , K + levels and Na + -K + ratio with BP by quantifying effects of adjustment for BMI and by exploring possible interactions of these variables with BMI in relation to adverse health complications.

Inclusion criteria
All the normotensive and non diabetic individuals of either gender between the age of 18 to 65years who came to the OPD of Base hospital, Srinagar, Garhwal and volunteered to participate were included during the period of study.

Exclusion criteria
Patients in the age <18years or >65years, pregnant subjects, patients with diabetes, hyperlipidaemia, subjects on any .medication therapy, any congenital or acquired condition which affects Na + and K + blood levels and BMI will be excluded from the study.

Methods of Data Collection
After obtaining the informed consent, person's biological data viz.age, sex, weight, height and blood pressure were recorded.

Height
The subject is asked to stand on a horizontal plane with heals together, stretching upwards to the fullest extent and hands loosely handling down.The marked Frankfurt plane is made horizontal.The anthropometer is kept vertical with left hand of the investigator and the horizontal sliding arm is made to touch vertex of the subject.The reading was noted at horizontal arm on anthropometer from the level on which subject was standing (Dudekula et al., 2012).

Weight
To measure subject's weight, standard portable weighing machine was used.The subject was asked to stand erect with minimum clothing and barefoot on weighing machine and the weight was noted (Dudekula et al., 2012).

Blood Pressure Measurement
Subjects were seated in a chair with their back supported and their arms rested at heart level.Measurement was performed with the subject not having ingested coffee or smoked for 30 minutes and after at least five minutes of rest.The first Korotkoff sound for Systolic Blood Pressure (SBP) and fifth Korotkoff sound for Diastolic Blood Pressure (DBP) were recorded by the height of mercury column on sphygmomanometer and the two readings were taken and averaged (Syed and Qureshi, 2012).Mean Arterial Pressure (MAP) was calculated by the formula: MAP = [(2 × DBP) + SBP] ÷ 3.

Biochemical Analysis
Venous blood samples were drawn, centrifuged and analyzed (by commercially available kits) for estimation of electrolytes (Na + and K + ).The analysis of serum electrolytes was carried out in auto-analyzer for Na + and K + using ion selective electrode measurement (Jankunas, 2002).
The data was tabulated to make it easy to understand and use for further purpose.

Data collection procedure
Data was collected in the form of case examination record sheet which would be preserved for any future use.All data would be kept confidential and no citing of any individual's identity would be done at any point of time during research or thereafter.

Statistic Analysis
Statistical differences between the BMI and other parameters viz.Na + , K + , Na + /K + ratio, SBP DBP and MAP were tested by one way analysis of variance (ANOVA) followed by post hoc multiple comparisons and Pearson's correlation.P values were calculated referring to the appropriate tables.Values of P<0.05 were considered as statistically significant.

OBSERVATIONS & RESULTS
A total of 204 healthy volunteer were studied who came to the OPD and willingly choose to take part in the study.The information regarding the distribution pattern of participants as per gender, diet and life style is provided in Figure 1 and number of participants under each BMI category is shown in Figure 2.  Analysis by Pearson's correlation coefficient, a negative correlation of BMI with serum Na+ levels & K + levels was seen which was statistically significant (p<0.05).Comparing with each other, BMI showed a more negative correlation with Na + level than K + level.On analysis with ANOVA, the effect of BMI on SBP, DBP and MAP was found to be statistically significant (p<0.05).When comparing the Obese BMI category with the Normal with reference to Systolic Blood Pressure and done by post hoc multiple comparison test, it was found to be statistically significant (p<0.05).Similarly on Pearson's correlation coefficient, the serum Na + is shown to be more positively related to SBP and the serum K + to be negatively related to SBP which was found to be statistically significant (p<0.05).No statistical significance was found when comparing BMI with gender, diet and life style.

DISCUSSION
There are very few studies which relate BMI with serum sodium and potassium and therefore this study was under taken to find out the correlation between BMI and serum electrolyte sodium and potassium in all the age groups.
Data analysis in one of the study indicated that serum Na + level was positively related to BMI and to systolic and diastolic BP in pre-HTN group (Syed and Qureshi, 2012) while our study partially contradicts with above study in relation to Na + with BMI where it shows a more negative correlation of serum Na + and K + with BMI.With reference to Syed and Qureshi, 2012, in our study, the serum Na + is shown to be more positively related to SBP in addition to that we found the serum K + to be negatively related to SBP.
The obesity has many adverse effects on haemodynamics thus explaining the relation of increase in BMI with increase in blood pressure.One of the study states that excessive adipose accumulation leads to increased circulating blood volume which results in higher cardiac output caused by stroke volume in obese patients but a lower level of total peripheral resistance at any given level of arterial pressure (Alpert, 2002), although, heart rate is typically mildly increased because of increased sympathetic activation (Messerli et al., 1987).The above study support our finding of negative correlation of BMI with serum Sodium and Potassium which could be due to haemodilution resulting from increased blood volume in high BMI or obesity.
Our study showed that BMI is positively related to SBP and DBP which was found statistically significant (p<0.05).In another study which added further evidences for the direct relationship between blood pressures and BMI, blood pressures and age, as well as blood pressures and sodium concentrations (Lufti, 2012).As per INTERSALT study, the correlation coefficient was higher when correlating BMI with blood pressure thus pointing to the risk of developing hypertension in those having high BMI (Dyer, 1990).
It can be stated that the an increase in blood volume in high BMI (overweight and obese) can be one of the factor in increasing the blood pressure and at the same time may be responsible for lowering serum Na+ and K+ levels due to haemodilution which correlates with the findings of our study.

CONCLUSION
Our study concludes that BMI has an association with serum Na + and K + levels.BMI has a definite role in the development of hypertension.Awareness shoud be made about the BMI and its association with blood electrolyte levels in mediating cardiovascular complications.Moreover stress should be given to have BMI within the normal range and preventive measure should be advised especially the lifestyle changes to the community at large.

ACKNOWLEDGEMENT
We are grateful to the people of Srinagar, Garhwal for voluntarily participating and co-operation in the study without them this study would not have been possible.

Fig. 1 :
Fig. 1: Gender, diet and life style distribution of participants.

Fig. 2 :
Fig. 2: Gender, diet and life style distribution of participants.

Financial
support and sponsorship: Our sincere thanks to the Principal, VCSGGMS & RI, Srinagar, Uttarakhand and the medical superintendant of HNB Base Hospital, Srikot, Srinagar who supported the ICMR STS Project 2014 and gave permission to conduct the study.
cross sectional study was conducted by the Department of Pharmacology, Veer Chandra Singh Garhwali Government Medical Science and Research Institute at HNB Base Teaching Hospital, Srikot, Srinagar, Pauri Garhwal, Uttarakhand between 15 July 2014 to 15 September 2014 as part of Short Term Studentship Project 2014 approved and sponsored by Indian Council Of Medical Research, New Delhi (Reference ID: 2014 -02746).Participants were provided written or verbal (if not literate) informed consent after the approval of all study procedures by institutional Ethics Committee (Review Letter No. IEC/VCSGGMSRI/27/2014 dated 08/7/2014).All procedures were conducted in accordance with institutional ethical guidelines.