**4. Why study homocysteine in the COPD patient?**

Smoking is by consensus the most important risk factor in the development of COPD (GOLD 2010). Cigarette smoking causes elevation of plasma HCY (Bazzano et al 2003, Kai et al 2006) though the effect may be variable (Nygard 1998). Smoking is also a risk factor for the development of vascular disease and cessation of smoking contributes to cardiac risk reduction (Ford 2007). Several studies have linked and continue to link homocysteine with cardiovascular risk (Homocysteine Studies 2002, Givvimani 2011, and Tehlivets 2011). Since both cardiovascular disease and COPD share a common cause (Izquierdo et al, 2010) which itself causes hyperhomocysteinaemia, it is reasonable to expect that COPD should be associated with elevated HCY.
