An increasing number of women of reproductive age follow vegan diets.

Because vegan diets are deficient in a number of essential nutrients, guidelines address the necessity of supplementations such as iron, zinc, and vitamin B12.

However, the risk of riboflavin (vitamin B2) deficiency is not properly addressed. We report a case of a male neonate with a life-threatening hypoglycaemia and lactic acidosis due to severe riboflavin deficiency.

The mother followed a strict vegan diet with intermittent use of supplements (folic acid, vitamin B12, vitamin D, omega 3). This case highlights the importance of adequate counselling of all pregnant women adhering to vegan diets to ensure sufficient intake of essential nutrients and vitamins, including riboflavin.