The European Union's highest court has ruled that Denmark may set stricter limits on cancer-causing substances in food than the European Commission allows.   In 1995, the EU passed a law setting community-wide limits on food additives. Denmark opposed the law at the time, on the grounds that it failed to meet health requirements for nitrates, nitrites and sulphites. Denmark has tougher limits on such additives, which may cause cancer or lesions in the digestive tract, than the rest of the EU, reported Reuters.