If you shun the sun, suffer from food allergies, and don’t get enough fruit and veggies, it’s likely you may be vitamin deficient. In fact, 46 percent of United States adults aren’t getting enough vitamin C. According to The Cleveland Clinic, 42 percent of people are vitamin D deficient, and 90 percent are not getting enough vitamin E. Getting too little of these essential vitamins can be dangerous, even life-threatening.