An American blogger who documented her son’s health struggles online has been arrested for his murder.

Lacey Spears of New York allegedly pumped a lethal amount of sodium into her 5 year old son’s stomach through a tube when he was admitted to hospital last January.

The New York Times reports authorities became suspicious when the boy was found to have died from sodium poisoning, and had been investigating the case for more than a year.

“This mother was intentionally feeding her son salt in toxic levels,” said Assistant District Attorney Doreen Lloyd in court this week.

Computer records showed that Ms Spears had searched the internet to research what effect salt would have on her son, said Ms Lloyd.

The boy’s mother, who is charged with second-degree murder and first-degree manslaughter, could face a sentence of 25 years to life in prison if found guilty.

Authorities said that they believed Ms Spears suffers from Munchausen syndrome by proxy  , a mental illness in which a parent harms their child in order to receive sympathy from others.

Ms Spears wrote about her son’s illness on her blog regularly in emotional posts she shared with her followers.