Beverley Thahane, from Telford in Shropshire, only learned little Noah had a severe vitamin D deficiency just before he died in January.
He had been suffering seizures and doctors struggled to diagnose the reason why.
She told the BBC: "He started changing colour again and I knew he was going to have another seizure but unfortunately it ended up being a heart attack.
"Vitamin D is a silent killer. I am without a child now and the sickness was silent, nobody knew, nobody picked it up.'
Rickets is a condition which affects bone development in children.
It causes the bones to become soft and weak, which can lead to deformity and poor growth.
Rickets is a condition normally associated with the Victorian era.
From late March to the end of September, most Brits should get all the vitamin D they need from sunlight.
However, people with darker skin need more sun exposure to see the same effect.
Ms Thahane added: "As people of colour we do know that in a country like this, with weather like this, there is not a lot of sunshine.
"But we don't think much about it, we didn't know the severity of it, that it can actually kill somebody."
Cases of rickets are on the rise in Britain - with financial inequality and bad diets thought to be to blame.
Common skeletal deformities include bowed legs, curved spines and thickened ankles, wrists and knees.
Kids with rickets are also more likely to fracture their bones.
Warning signs include painful bones, a child waddling instead of walking, skeletal deformities, dental problems, poor growth and development, and fragile bones.
Rickets is normally caused by a lack of vitamin D or calcium.
The best source of vitamin D is to get outside and enjoy the sun, but it's also found in some oily fish, egg yolks and cheese.
One doctor recently warned that a generation of 'stay-indoors teenagers' are putting themselves at risk of bone and heart disease because they're not getting enough sunlight.
One in five Brits are now vitamin D deficient, with doctors advising us to take supplements during the long winter months.
Babies need 8.5-10mg of vitamin D-a-day and, from the age of one, we all need 10mg-a-day.