**Core Concept**
Excess cortisol causes a range of systemic effects due to its role as a glucocorticoid hormone. Cortisol is a potent anti-inflammatory agent that also influences glucose metabolism, electrolyte balance, and cardiovascular function. Chronic exposure to elevated cortisol levels can lead to a condition known as Cushing's syndrome.

**Why the Correct Answer is Right**
Cortisol acts through the glucocorticoid receptor (GR) to induce gene expression and modulate various physiological processes. In excess, cortisol can lead to the redistribution of body fat, particularly in the abdominal region, and cause hyperglycemia due to increased gluconeogenesis and reduced glucose uptake in peripheral tissues. Additionally, cortisol can cause hypertension, hypokalemia, and osteoporosis due to its effects on the renin-angiotensin-aldosterone system, mineralocorticoid receptors, and calcium metabolism.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cortisol does not typically cause anemia in excess. While cortisol can affect erythropoiesis, it is more commonly associated with polycythemia due to increased erythropoietin production.
**Option B:** This option is incorrect because cortisol does not typically cause hypothyroidism in excess. Cortisol can affect thyroid function, but it is more commonly associated with thyroid suppression or thyroid storm in the context of iatrogenic Cushing's syndrome.
**Option C:** This option is incorrect because cortisol does not typically cause hyperkalemia in excess. Cortisol can cause hypokalemia due to increased potassium excretion in the urine.

**Clinical Pearl / High-Yield Fact**
A key feature of Cushing's syndrome is the development of "buffalo hump" - a distinctive accumulation of fat in the upper back, often accompanied by moon facies and truncal obesity. This is a classic clinical correlation to remember for exam purposes.

**Correct Answer: C. Cushing's syndrome**