In one study, researchers measured blood levels of vitamin D in 3,262 Chinese men and women from Beijing and Shanghai, aged 50 to 70, and found that 24 percent were low and 69 percent were deficient in vitamin D. Among those low or deficient, 42 percent had metabolic syndrome. Chances for insulin resistance and metabolic syndrome increased as vitamin D levels fell, especially in those who were overweight or obese. Doctors said the findings were consistent with other studies in Western populations.