In non-diabetic and non-hypertensive individuals, maintaining a low level of Cystatin C was associated with a decreased risk of cognitive decline compared with maintaining a medium level.<h4>Conclusion</h4>This study found that maintaining a low level of Cystatin C is associated with a lower risk of cognitive decline in non-diabetic individuals, while in older individuals with diabetes, maintaining a low level of Cystatin C increases the risk of cognitive decline. The gene discussed is CST3; the disease is diabetes mellitus.