Why malnutrition can go unnoticed, and what that means for our health

More than 2 billion people worldwide suffer from nutrient deficiencies, most of them in the Global South. The health consequences can be devastating. Some 50,000 deaths can be attributed to malnutrition in Germany each year, according to the German Society for Nutritional Medicine (DGEM). "In most cases, you don't notice anything at first," said Matthias Pirlich, a nutritional expert and internal medicine specialist, who once served as DGEM vice president.

"You could have a severe vitamin D deficiency for months before any symptoms appear at all. The same applies for vitamin B12. By the time symptoms appear, such as nerve damage, it's already too late." A long-term B12 deficiency can damage the spinal cord, leading to numbness in the limbs, muscle weakness or even paralysis. Less common deficiency-related brain damage can cause memory loss and mental health issues.

Vitamins, along with various minerals such as calcium, magnesium, iron, iodine and zinc, are classed as micronutrients. The body needs to source them from food, as it cannot produce them itself.