A pathologist has said a New Zealand woman's eight-litre-a-day Coca-Cola habit probably contributed to her death, a conclusion that led the soft-drink giant to note that even water can be deadly in excessive amounts.

Natasha Harris, 30, of Invercargill, died from a heart attack in February 2010.

A pathologist said Natasha Harris's Coca-Cola habit probably contributed to her death in 2010. Photograph: AP

Dr Dan Mornin testified at an inquest on Thursday that Harris probably suffered from hypokalemia, or low potassium, which he thinks was caused by her excessive consumption of Coke and overall poor nutrition, Fairfax Media reported.

Symptoms of hypokalemia can include abnormal heart rhythms.

Mornin said toxic levels of caffeine, a stimulant found in cola, also may have contributed to her death.

Harris's partner, Chris Hodgkinson, testified that Harris drank between 8 and 10 litres of Coke every day.

"The first thing she would do in the morning was to have a drink of Coke beside her bed and the last thing she would do at night was have a drink of Coke," Hodgkinson said. "She was addicted to Coke."

Hodgkinson said she ate little and smoked about 30 cigarettes a day. In the months before her death, he said, Harris had experienced blood pressure problems and lacked energy.

He said that on the morning of her death, Harris helped get her children ready for school before slumping against a wall. He called emergency services and tried mouth-to-mouth resuscitation but couldn't revive her.

Another pathologist, Dr Martin Sage, said in a deposition that "it is certainly well demonstrated that excessive long- or short-term cola ingestion can be dramatically symptomatic, and there are strong hypothetical grounds for this becoming fatal in individual cases."

With the evidence in the case now complete, the coroner's office will compile and issue a final report into the death.

Lisa te Morenga, a nutritionist at the University of Otago, told the Associated Press that excessive consumption of any type of liquid in a cool climate would be likely to play havoc with the body's natural systems and balances.

Karen Thompson, a spokeswoman for Coca-Cola Oceania, said in a statement that its products were safe.

"We concur with the information shared by the coroner's office that the grossly excessive ingestion of any food product, including water, over a short period of time with the inadequate consumption of essential nutrients, and the failure to seek appropriate medical intervention when needed, can be dramatically symptomatic."