Kidney function is a health issue that is often left out of popular discussion and debate however compromised kidney function is an important health concern for many people. For instance the effects of hypertension upon the kidneys can be disastrous. Fragile microscopic renal blood vessels cannot tolerate an increased pressure of blood and fluids passing through them over the long-term. Diabetic nephropathy is one of the most common causes of kidney dysfunction. An obvious result of the chronic hyperglycemia associated with diabetes is the formation of advanced glycation end products (AGEs). In effect the tiny renal tubules become sticky with sugar we can think of this as the vessels becoming hard and brittle like glass rather than soft pliable and accommodating as with healthy blood vessels. Couple the increased fragility of these tubules with increased pressure of the blood passing through them and it sets up a situation that the kidneys cannot keep up with.

The connection between hypertension and blood glucose is even more insidious than it seems. The hypertension that often accompanies diabetes or chronic hyperglycemia even in the absence of diagnosed diabetes isn't only a function of glycated hemoglobin and glycated vasculature. Hyperglycemia leads to an increased retention of sodium through an effect on the proximal convoluted tubule in part via sodium-glucose cotransporters (SGLTs). The kidneys reabsorb glucose from the glomerular filtrate and return it to the body's circulation. The capacity of these transporters is one of the limiting factors in the kidney's ability to reabsorb glucose. As plasma glucose concentrations approach 180-200mg/dL glucose begins to appear in the urineone of the classic signs of diabetes. However the kidneys will continue to reabsorb additional glucose and therefore sodium even when blood glucose is abnormally elevated as not all the excess will be excreted.

As if the negative downstream effects of chronic hyperglycemia weren't bad enough in diabetics and non-diabetics alike it's not just the hyperglycemia producing these effects but also the hyperinsulinemia. Insulin has long been known to affect sodium dynamics in the body. Insulin decreases the urinary excretion of sodium in hypertensive patients as well as normotensive controls. This is likely why diabetes hypertension and chronic kidney disease are often comorbidities and might also explain why even in non-diabetics chronically elevated insulin levels and hypertension cluster together (in metabolic syndrome). Patients with essential hypertension have higher fasting and postprandial insulin levels than normotensive people and studies have demonstrated a direct relationship between plasma insulin levels and blood pressure.

The inhibition of sodium excretion by insulin may be exacerbated by low potassium levels. This is not surprising given the crucial relationship between sodium and potassium at the cellular level. Researchers have determined that there is a role for potassium in mitigating insulin-induced sodium retention. A small but demonstrative study involving six healthy young males infused with insulin with and without a potassium infusion showed that the presence of potassium largely prevented the 38% decline in urinary sodium excretion that occurred without the potassium. Other studies lend further evidence to the role of hypokalemia in sodium retention via the effects of insulin.

Clearly the relationship between elevated blood glucose hyperinsulinemia and kidney health is a complicated one. But the good news is there is a relatively simple way of improving all three at the same time by following a reduced-carbohydrate diet that includes plenty of fresh potassium-rich vegetables low-glycemic fruits and healthy fats the latter of which have virtually no effect on glucose and insulin levels. Whole unprocessed foods tend to contain very little sodium so this type of diet presents a multifaceted strategy for supporting kidney health as it directly relates to managing blood glucose and insulin and mitigating the damaging effects that occur when these are chronically elevated.