Twins might be identical or non-identical in appearance but their behaviour and characteristics have always been non-identical. Among nutrients too, it is not wrong if we call Sodium and Potassium as twins owing due to the strong relationship between them. These two together play a huge role in regulating blood pressure and are closely involved in bone health. Both of them are electrolytes needed for normal body functioning, fluid balance and blood volume maintenance in our body. The very question now is how much of these nutrients are needed for a balanced life?
Molecular pumps pull potassium into cells and push sodium out of them to create a chemical battery that drives the transmission of signals along the nerves thereby empowering muscle contraction. An imbalance in sodium-potassium levels lays the foundation for a number of health problems-too much of sodium content and too little of potassium can raise blood pressure levels but such imbalances have become problematic recently. Long long ago, when man roamed the Earth in search of food he consumed more of fruits, vegetables, leaves, flowers, roots and plant sources (our so-called Palaeolithic diet) which provided humans with abundant potassium and minimal sodium. But now, sodium consumption has gone way above normal limits with the inclusion of processed foods and high-salt meals in our diet whereas potassium levels are far below recommended values due to minimal consumption of produce and other plant-based foods.
The body tries to maintain sodium-potassium balance with what we feed to it. Higher sodium levels and lower potassium levels worsens health as the body tries to hang on to the available nutrient, sodium, to compensate for the missing nutrient, potassium. This complicates the situation even more as blood pressure shoots up and the heart muscles are forced to work harder. Its possible to throw out sodium by bringing in more potassium into our system and this proves to be extremely useful in helping the heart and arteries as well. Its sad that the relationship between sodium and potassium and vascular function has not been brought into the limelight as required.
Cardiovascular disease is widespread in our world today owing to different reasons. Increased arterial stiffness and wave reflection are independent risk factors that increase the risk of cardiovascular events. Studies show that meals high in sodium content increase augmentation index in normotensive adults and such prolonged intake (more than 2 weeks) in young, healthy males with normal BP increase wave reflection and carotid BP. Thereafter, sodium restriction for the next two weeks improved carotid arterial compliance and augmentation index in elderly people with systolic blood pressure. But potassium’s effect on vascular function has not been explored much, even in those research studies that have dealt with it have inconclusive effects seen and some showed no change in arterial stiffness as well. Multiple trials have given hints that high urinary excretion ratio affects BP levels and cardiovascular disease risk which makes researchers even more interested in knowing the link between sodium and potassium interaction.
Effect of Sodium & Potassium Interaction on Arterial Stiffness
One study specialized in understanding this link between sodium and potassium and their effect on arterial stiffness. The study included 36 participants who were healthy and young aged around 24 years. Those who were obese, smoking, under medications for cardiovascular/hypertension, with history of hypertension, cardiovascular disease, diabetes or renal impairment were disallowed from participating. All the participants were given instructions on the recommended portion sizes and asked to eat as they would normally and include two weekdays and either of the weekend days in the record provided by the research team for noting down eating schedules. Urine samples were collected for calculating free water clearance and fractional excretion of sodium, potassium and chloride. Physical activity levels of each of the participants were tracked and the measurements were noted down. All the participants were informed not to exercise for 24 hours, eat for 4 hours and drink alcohol/caffeine for 12 hours prior to testing.
Radial artery waveform was recorded using a applanation tonometry with the help of high-fidelity strain-gauge transducers placed over the radial artery. Central pressures and augmentation index (AI) were obtained from the synthesized wave. AI indicates wave reflection and is influenced by arterial stiffness. Reflection magnitude (RM) was calculated as the ratio of the amplitudes of reflected/forward waves. Carotid-artery pulse wave velocity (PWV) was calculated using tonometry to record carotid artery and femoral artery waveforms simultaneously. Blood samples were taken from all the participants to measure plasma haemoglobin levels.
All participants had normal BMI ranges, normal iron status and electrolyte levels. Physical activity assessment showed that all the participants expended 1025±279 kcal/day above resting energy expenditure. Average BP measurements were 117±2/63±1 mm Hg. All the subjects consumed around 2200 kcal/day where carbs provided 50% of the energy requirements, 31% were from fats and 18% was from proteins. Women consumed comparatively lower calorie numbers. Sodium intake was around 3763 mg/day which is well above the recommended levels while men consumed more than women. Potassium intake was around 2876 mg/day which is well below the recommended 4700 mg/day but there was no difference between both the genders in terms of potassium consumption. Sodium and potassium intake matched urinary excretion data suggesting that excretion reflects dietary intake. Sodium to potassium ratio was 1.4±0.1 and this is well above recommended numbers of 0.49.
Average AI was 2.2% and PWV was 5.2 m/s with females having higher AI rates than males. Though no correlation was found between sodium excretion and AI a significant inverse correlation was found between potassium excretion and AI. There was a significant relationship between sodium/potassium excretion ratio and AI, Tr was linked to potassium excretion and those with decreased potassium intake exhibited shorter time delay of the reflected wave. The link between potassium excretion and PWV showed that those with greater potassium intake have a slower velocity but there were no similar results seen between sodium/potassium excretion ratio and PWV. RM, the ratio of reflected and forward waves was significantly linked with sodium/potassium excretion ratio but not either of the two confirming that both sodium and potassium intake might be important mediators of wave reflection.
The study clearly indicates that potassium imposes greater influence on wave reflection in healthy, young adults- lower potassium excretion was linked to greater wave reflection and pulse wave velocity was faster. The China Salt Substitute study compared the effects of a potassium substitute containing 25% potassium chloride to regulate salt levels in individuals with higher risk factor for vascular disease over a 12-month period. Though this substitute incurred time delay in wave reflection there was no changes in AI. Another study by Matthesan et al. probed into the impact of supplementation of 100 mmol potassium chloride daily for 28 days. All the participants had a standard diet consisting of 150 or 200 mmol of sodium depending on energy needs. Results showed a small but significant increase in PWV without changes in AI or BP in the study participants. Other studies looking into potassium effect on wave reflection found that decreased supplementation of potassium did not create much of a difference in results. In our present study, high potassium levels were fed and these were associated with lower AI and a slower PWV. Arterial stiffness plays a significant role in the relationship observed between potassium excretion and wave reflection by encouraging the speed up of reflected wave. There is an inverse relationship between potassium intake, wave reflection and arterial stiffness in young, healthy adults. Increasing potassium levels in the diet helps in reducing the risk of cardiovascular disease besides lowering blood pressure levels.
Lower Potassium Intake is Associated with Increased Wave Reflection in Young Healthy Adults: https://nutritionj.biomedcentral.com/articles/10.1186/1475-2891-13-39
Potassium and Sodium Out of Balance: https://www.health.harvard.edu/staying-healthy/potassium_and_sodium_out_of_balance
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