The 18th National Congress of the Communist Party of China in 2012 announced the strategic aim of "promoting balanced development of the population in the long term", which applies to the entire population, as well as its subgroups, including the "national defense population".

The national defense population refers to that part of the population fit enough to join the military. The national defense population is critical to providing "sufficient" and "effective" supply of human resources to defend the country. "Sufficient" means enough people in the proper age group who can be enlisted in the military, and "effective" generally means satisfactory physical health of the group. In rough terms they mean quantity and quality.

The availability of eligible candidates has long been a problem with the military. Despite its huge population, China suffers from a shortage of military personnel. Because of the family planning policy, which allows most couples to have only one child, an overwhelming majority of youths today are the only children of their families. Most of these youths are not keen to join the military, because they need to take care of their parents.

The lack of policy coordination has made the situation worse. For example, colleges began easing their admission criteria in 2000, enabling more high school graduates, mostly aged between 18 and 22, to seek higher education, while the conscription law continued to exempt or discourage college students from joining the military. As a result, a high percentage of youths were excluded from the national defense population. This situation lasted for a decade.

Even this shrunken national defense population is found wanting in terms of quality. Despite the rising nutrition standards in China, the physical health of many youths is not good enough for the military.

A report on Beijing's primary and secondary school students' health, issued in March 2014, showed 21.6 percent of them were overweight, of which 50.2 percent had high blood sugar levels, 46 percent had abnormal blood fat, 45.1 percent had fatty liver and 30.7 percent had high blood pressure. As if those were not enough, 49.77 percent of the primary school students and 81.19 percent of those in middle schools were near-sighted. No wonder, more than 60 percent of Beijing youths applying to join the army have failed to pass the health test since 2006.

In 2014, the State had to change the weight, height and eyesight requirements in order to recruit enough youths in the military. Modern wars may no longer demand fierce physical prowess, but bad health will prevent personnel from going through the necessary physical training and thus compromise the fighting capability of the military.

This trend is unlikely to be reversed without changing the family planning policy, which, as the most influential demographic policy of China, has caused many problems - the most prominent being the high percentage of single children and their reluctance to join the military.

The State pays a minimum subsidy of 600 yuan ($97) a year to rural parents who have only one child or two daughters. This subsidy is too small for rural parents to risk the death of their only child and thus prevents them from encouraging their offspring to join the military.

To have a sufficient and effective national defense population, the State needs to first establish a series of programs for senior citizens and risk-prevention mechanisms in a bid to offset the effects of the family planning policy.

The authorities have allowed couples who are single children of their parents to have a second child. But still the birth rate of second children has not seen any significant increase, because not all such couples want a second child. Therefore, it is time to further ease the family planning policy and allow more families to have a second child so that more youths can come forward to join the military without having to worry about who will take care of their parents.

The author is a professor at the PLA Family Planning Official Training Center. The article first appeared in Population Research.