Health insurer Aetna Inc. announced its profit fell 57% in the fourth quarter as healthcare costs increased, and the company sustained large capital losses. Aetna earned $194.7 million, or 42 cents per share, down from $448.4 million, or 87 cents per share. The Hartford, CT-based company spent 81.8% of its premium revenue on medical care in the quarter, compared to 80.3% a year ago.