One of the biggest threats to your retirement solvency may be the cost of health care and prescription drugs.A study by West Health and Gallup shows that in the past 12 months, seniors have withdrawn an estimated $22 billion from their long-term savings for health-care-related expenses. The average amount people pulled out was $3,789.The report, titled “The U.S. Healthcare Cost Crisis,” included a nationally representative survey of more than 3,500 adults.“Americans in large numbers are borrowing…