Swelling in the feet, medically known as peripheral edema, is common. For individuals with diabetes, however, it signals underlying health complications. Uncontrolled high blood sugar levels damage the body’s systems, increasing the risk of fluid buildup in the lower extremities. Edema is a physical manifestation of systemic issues and localized tissue damage.
Systemic Causes: Fluid Retention and Organ Stress
Persistent high glucose levels damage small blood vessels, including the delicate filtering units of the kidneys. This condition, known as diabetic nephropathy, impairs the kidneys’ ability to effectively remove waste and excess fluid from the bloodstream. When the kidneys cannot regulate fluid balance, the extra volume accumulates, leading to generalized swelling that gravity pulls toward the feet and ankles.
Diabetes also increases the risk of cardiovascular strain, specifically heart conditions like congestive heart failure. When the heart muscle cannot pump blood efficiently, blood flow slows down, causing blood to back up in the veins that drain the lower body. This pooling forces fluid to leak out of the vessels and into the surrounding tissues, resulting in noticeable edema.
High blood pressure, which frequently co-occurs with diabetes, further contributes to fluid leakage. Hypertension raises the pressure inside the capillaries, which pushes fluid out into the interstitial spaces of the feet. Impaired kidney function, a strained heart, and elevated vascular pressure combine to cause chronic, body-wide fluid retention that becomes most apparent in the feet.
Localized Damage: Nerve and Vascular Compromise
Sustained high blood sugar directly harms the nerves in the feet, a condition called peripheral neuropathy, which is the most common form of diabetic nerve damage. This nerve damage leads to a loss of protective sensation, meaning minor cuts, blisters, or sprains may go unnoticed. An undetected injury triggers an inflammatory response, resulting in localized swelling.
Neuropathy can also affect the autonomic nerves that control blood vessel function, causing them to lose their ability to constrict and dilate properly. This autonomic dysfunction leads to increased blood flow to the skin, which raises the pressure in the capillaries of the foot and promotes fluid leakage into the tissues. The resulting edema is a direct consequence of this impaired nerve-mediated blood flow control.
Diabetes causes both microvascular (small vessel) and macrovascular (large vessel) diseases that compromise circulation. Peripheral Arterial Disease (PAD), a macrovascular issue, involves the narrowing of arteries, which impairs oxygen supply and hinders fluid removal from the feet. Microvascular changes involve the thickening of capillary walls, which slows blood flow and contributes to fluid accumulation in the lower limbs.
Charcot foot is a severe complication where undetected injuries, due to neuropathy, lead to rapid bone and joint destruction. This condition is characterized by an acute inflammatory response that causes the foot to become hot, red, and severely swollen, often without significant pain. The swelling in Charcot foot is a sign of bone fragmentation and joint dislocation, requiring immediate medical intervention to prevent permanent deformity.
Acute Factors and Necessary Action Steps
Swelling can be a side effect of medications commonly prescribed to manage diabetes and its related conditions. Certain anti-diabetic drugs, particularly those in the thiazolidinedione class like pioglitazone, are known to increase fluid retention and cause peripheral edema. Medications for high blood pressure, such as calcium channel blockers, can also lead to swelling in the ankles and feet.
A sudden increase in swelling, especially if confined to one foot, can indicate a serious problem like a deep vein thrombosis (DVT) or a severe infection. Swelling accompanied by redness, warmth, pain, or fever may signal cellulitis, a deep bacterial skin infection that can rapidly spread. Because high blood sugar compromises the immune system and circulation, these infections can quickly become limb-threatening and require urgent care.
If you notice swelling, check your feet daily for any signs of injury or infection, using a mirror for hard-to-see areas. To manage mild, chronic swelling, elevate your feet above heart level several times a day and wear non-binding, properly fitted footwear. Immediate medical attention is necessary if swelling is sudden, involves only one leg, or is accompanied by red streaks, significant warmth, or systemic symptoms like fever, chills, or chest pain.