When a person has pernicious anaemia, this simply does not happen; instead, intrinsic factor isn’t produced and vitamin B12 is lost through excrement.
The exact cause of pernicious anaemia is still unknown, but it’s more often diagnosed in women around 60 years of age.
It’s also more prevalent in those with other autoimmune conditions, such as vitiligo.
Others may develop a vitamin B12 deficiency if they follow a vegan diet or have a very poor diet.