The phenomenon of "hidden hunger" affects more than two billion people globally. It has been centered on developing countries, but is becoming a growing public health concern in the wealthy world. There are several factors behind the rise but we believe the surge of interest in veganism is likely to become another major contributor.

Hidden hunger boils down to a chronic lack of essential micronutrients in the diet, such as vitamins and minerals. The effects of this may not be seen immediately, but the consequences can be severe. They include lower resistance to disease, mental impairment and even death.

Evidence of its rise in developed countries is starting to build. For example, iodine deficiency is the most common cause of preventable mental impairment and the UK ranks seventh among the ten most iodine-deficient nations.

Data from the US shows that more than one in four children lacks calcium, magnesium or vitamin A, and more than one in two children are deficient in vitamins D and E.

So why is this happening?

Well, the consumption of cheap, energy-dense, nutritionally poor and heavily processed foods, particularly by poorer people, is a major factor. Even when fresh produce is consumed, there appear to be fewer micronutrients available than was once the case. This is due to issues such as soil health, caused by poor agricultural management and climate change.

Now, the enthusiastic uptake of veganism can be added to that list. According to the Vegan Society, the number of people switching to a vegan diet in the UK has risen more than fourfold in the last decade. A study commissioned by the Vegetarian Resource Group revealed that nearly 5% of the US population are vegetarian and about half of these are vegan.

For the record, eating a plant-based diet may lower the risk of chronic disease and is good for the environment. However, poorly planned vegan diets, that do not replace the critical nutrients found in meat, can lead to serious micronutrient deficiencies.

Bone health is a concern for long-term vegans. Vegans are consistently reported to have lower intakes of calcium and vitamin D, with resultant lower blood levels of vitamin D and lower bone mineral density reported worldwide. Fracture rates are also nearly a third higher among vegans compared with the general population.

Omega 3 and iodine levels compare badly with meat eaters, as do vitamin B12 levels. Vitamin B12 is most often obtained from animal foods, and higher rates of deficiency have been found in vegans compared with other vegetarians and meat eaters.

The symptoms can be serious and include extreme tiredness and weakness, poor digestion and developmental delays in young children. Untreated, it can cause irreversible nerve damage and even a more modest lack of the vitamin may be bad for your health and increase your risk of heart disease.

B12 deficiency is quite common in pregnant women and in less-developed countries, but in terms of reported frequencies of deficiencies among vegetarians and vegans in developed countries, the data varies greatly in severity between age groups.

This is not an insoluble problem. Vegans can prevent micronutrient deficiency by taking care to consume fortified foods (food with added vitamins and minerals) and by taking supplements. But supplement use is often resisted by those on a plant-based diet and they have been reported to interfere with the absorption of other important nutrients.

Also, plant-derived vegan supplements tend to have low biological activity in humans. For example, studies show that vegan-friendly vitamin D2 supplements are less effective in raising blood vitamin D levels than the more widely used vitamin D3 supplements. Other supplements, such as vitamin B12, may be largely inactive in the body.

"Hidden hunger" is widely recognised in the developing world and is being addressed by well-organised and large-scale bio-fortification programmes. Hopefully the challenge offered by the rise of veganism will help drive a focus on hidden hunger in the West.