It’s quite well known that the growth in human height in most developed countries has stagnated. This is easy to explain and isn’t particularly worrisome. Human height is a product of underlying genetic potential, as influenced by the environment. As the diet of a nation improves, its people’s adult height should increase, up to a limit, as when all nutrient shortages are addressed, little more gains in height are to be expected.

On the other hand, in recent years it has been observed that despite simultaneous ongoing economic development, in many countries human height is declining again. Most worrisome perhaps is the rapid pace at which human height is declining in these nations. In some countries, decades of progress has been eradicated in a few years.

Consider the case of Nigeria below:

As can be seen here, by 1996, average male height is back to a level last seen in 1941.

Ethiopia has similarly been affected by a downturn much steeper than the initial rise in height:

Egypt has similarly seen an enormous decline in height, a typical case of Ugo Bardi’s Seneca cliff:

Not all poor nations are affected, China, Brazil and many others are still booking gains in height. It is however, a problem that affects nations collectively home to hundreds of millions of people.

What could explain this mysterious problem? Economists who look at Nigeria or many of the other African nations affected by this problem would see countries that were plagued by economic stagnation for decades, but now seem to be rapidly expanding their economies.

The authors of the study suggested that changing dietary habits may play a role, as well as collapsing health care system. This seems the most likely possibility to me. In particular, it’s worth noting that people in much of Africa depend upon bushmeat as their main source of protein.

As bushmeat is depleted, people are forced fill their diet with other foods. One source of nutrition that’s very popular in Africa is cassava, which is filled with cyanide. Chronic cyanide exposure however is known to cause a decline in growth, as well as cognitive problems. None of these explanations however could possibly explain what’s happening in Egypt. Egypt has no bushmeat, nor do Egyptians eat cassava.

It’s somewhat hard to draw any strong conclusions on what could have led to this sudden and rapid reversal in human height. One factor that may be relevant is the spread of smoking in much of the third world, as it’s known that second hand smoke exposure reduces the growth rate of young children. It’s also possible that a decline in breastfeeding rates played a role.

Another factor that may be important is a rise in vitamin D deficiency. If rural women and children were more active outside, increasing urbanization may have led to an increase in vitamin D deficiency that stunts growth. It’s known that vitamin D deficiency is epidemic throughout the third world.

Finally, the main and most important factor to be considered would have to be be a drastic reduction in the quality of people’s diet. If people’s diet has become less diverse, they would be expected to suffer a variety of nutrient deficiencies that impact their growth. Fresh fruit and vegetables are difficult to store and thus rather expensive. Urbanization may lead people to grow dependent on a much worse diet.