After a cold winter with little sunlight lack of vitamin D is common, but how do you know if your levels are too low? Traditionally lack of Vitamin D is linked with poor bone health, but new studies suggest that milder deficiency may also be linked to asthma, some cancers and diabetes. Dr Mark Porter investigates and hears from a night shift worker who had such excruciating pain in her hands she thought that she had arthritis - when her doctor checked for vitamin D levels, 3 weeks of supplements cured the pain. Show less