Difficult one to call. If the elastic is too tight it will constrict the leg's circulation and yes it could encourage varicose veins. On the other hand a suitable evenly applied and not too tight elasticated pressure can be beneficial to the leg's circulation hence the popularity of support hose and elasticated flight socks. I've had a varicose veins op 14 years ago and have varicose veins developing again so am always careful not to have the hose elastic too tight. IMHO varicose veins are more likely to arise from doing a job where you are standing a lot, for example a sales assistant.