World Health Organisation advice has prompted Hong Kong food safety authorities to warn people with heart problems to avoid consuming four types of milk powder manufactured by Fonterra.
The agency warned against Anlene Phyto K milk powder - which contains vitamin K - after advice from the WHOthat the milk powders may interfere with prescription drugs for blood-thinning.
It said the level of vitamin K in the milk and yoghurt products could pose health risks to people taking Warfarin, a blood-thinning agent commonly taken by people with heart disease.
Patients taking Warfarin were advised to talk to their doctors before taking any of the products.
Fonterra also launched the product in powdered format in Singapore and Malaysia last year.
New Zealand's Food Safety Authority said in August that Fonterra must add a warning label to the new vitamin K-enriched milk and yoghurt to reduce the risk for people taking Warfarin.
Fonterra's Anlene brand has been marketed in Asia for bone health for many years, but is not fortified with vitamin K in all its markets.
The Phyto K range was launched in New Zealand in May.
Vitamin K - which has improved bone mineral density and reduced the incidence of bone breaks in some studies - is not allowed to be added to most foods, including milk, under New Zealand's food regulations.
Instead Fonterra has marketed its products as a dietary supplement, a common strategy where manufacturers do not make therapeutic claims for a product.
But the New Zealand food safety officials said people on anti-coagulation medication might not expect vitamin K - normally found in leafy green vegetables - in dairy products and so warnings were necessary.
In Hong Kong, where the fortified milk powder is sold in four formulations, Queen Elizabeth Hospital head of cardiac services Dr Chiang Chung-sheung told the Standard newspaper that heart patients should not consume any of them.
