In evaluation studies, researchers have linked vitamin D deficiency to melancholy, notably in older adults . One study examined the affiliation between vitamin D levels and back ache in additional than 9,000 older girls. The study found that girls with blood levels lower than 20 ng/ml or 21–29 ng/ml were more likely to complain of fatigue than those with blood levels over 30 ng/ml . Case research have shown that very low blood levels can cause fatigue that has a severe negative effect on quality of life . People who live near the equator and get frequent sun exposure are less prone to be poor, as their pores and skin produces enough vitamin D to fulfill their bodies’ needs.