This study investigates the causal relationship between serum homocysteine levels and cardiovascular diseases, including ischaemic heart disease, deep vein thrombosis, pulmonary embolism, and stroke. Using a meta-analysis of genetic and prospective studies, the researchers found significant associations between elevated homocysteine levels and increased risk of these diseases. Genetic studies showed that individuals with a mutation in the MTHFR gene (which increases homocysteine levels) had higher risks of ischaemic heart disease, deep vein thrombosis, and stroke. Prospective studies also found a significant association between higher homocysteine levels and increased risk of these diseases. The results suggest that the association between homocysteine and cardiovascular disease is causal. The study estimates that reducing homocysteine levels by 3 μmol/l (achievable through increased folic acid intake) could reduce the risk of ischaemic heart disease by 16%, deep vein thrombosis by 25%, and stroke by 24%. The study concludes that lowering homocysteine levels could be a simple and effective way to prevent cardiovascular disease.This study investigates the causal relationship between serum homocysteine levels and cardiovascular diseases, including ischaemic heart disease, deep vein thrombosis, pulmonary embolism, and stroke. Using a meta-analysis of genetic and prospective studies, the researchers found significant associations between elevated homocysteine levels and increased risk of these diseases. Genetic studies showed that individuals with a mutation in the MTHFR gene (which increases homocysteine levels) had higher risks of ischaemic heart disease, deep vein thrombosis, and stroke. Prospective studies also found a significant association between higher homocysteine levels and increased risk of these diseases. The results suggest that the association between homocysteine and cardiovascular disease is causal. The study estimates that reducing homocysteine levels by 3 μmol/l (achievable through increased folic acid intake) could reduce the risk of ischaemic heart disease by 16%, deep vein thrombosis by 25%, and stroke by 24%. The study concludes that lowering homocysteine levels could be a simple and effective way to prevent cardiovascular disease.