Losing a child could increase the risk of developing multiple sclerosis, a study shows.
Stress has been linked to the development of multiple sclerosis
Researchers at Aarhus University in Denmark found parents who had lost a child unexpectedly were 50% more likely to develop MS than parents who had not.
The team looked at over 300,000 families on the Danish National Register.
The researchers believe the findings could lead to a better understanding of the condition and new treatments.
Around 85,000 people in the UK have MS.
Previous studies have linked stress to a worsening of the condition.
Dr Jiong Li and colleagues looked at parents who had lost a child because it is one of the most stressful occurrences in a society with low infant mortality.
"We hypothesized that, if stress causes MS, only severe stresses are likely candidates, because MS is a rare disease."
The researchers looked at 21,062 parents who had lost a child under 18, and 293,745 who had not, and followed them for almost ten years.
Out of the parents who had lost a child, 28 developed multiple sclerosis, while MS was diagnosed in 230 of the other parents.
They found age, sex, and the age of the child when they died had no bearing on the risk of developing the condition.
Dr Li said the risk was higher though, among parents who had lost a child unexpectedly.
"This is more evidence that stress plays a role in the disease, because losing a child unexpectedly is considered to be even more stressful for parents."
He said the findings could lead to new treatments for MS by discovering how processes in the body are affected by stress.
Christine Jones, Chief Executive of the MS Trust told BBC News Online "thousands of people who have MS believe that stress does contribute in some way, either by triggering or exacerbating the condition."
"There has always been controversy over the relationship between stress and multiple sclerosis. This Danish research is extremely interesting and will no doubt contribute further to the debate."
MS is an autoimmune disease that affects the central nervous system. It occurs when the protective sheath surrounding the nerve fibres, called myelin, is damaged, causing the messages between the brain and the body to be disrupted.
Sufferers can experience mild or chronic forms of the disease, meaning some people are able to lead a normal life while others become severely disabled.