An extraordinary sequence of events must take place before a baby can cry out for the first time. Infant development researchers refer to the moments that surround this milestone as the "transition to extrauterine life." Indeed. The baby is delivered, still attached by its lifeline, the umbilical cord, to the remarkable but temporary organ, the placenta, that has sustained the fetus and met all of its physiological needs. Within seconds after this connection has been abruptly broken, the baby must breathe on her own for the first time so that her circulatory system can deliver oxygen to all of the tissues throughout her body. Though this dramatic shift seems nothing short of miraculous, the great majority of babies leap across this transition with nothing more than a loud cry of recognition.

Lung development proceeds in five main stages, the earliest taking place in the embryo between three to seven weeks gestation, explains Susan Tucker Blackburn, in Maternal, Fetal, & Neonatal Physiology. Rudimentary fetal breathing movements also start early in gestation and steadily grow in strength and frequency. Lung development throughout gestation will be stimulated by the mechanical stretching caused by these movements. The fifth stage, which involves the maturation of the tiny air sacs called alveoli, extends from 36 weeks gestation through 2 years. These alveoli are the site of gas exchange, but only about 15% are mature by birth.

The diameters of the alveoli double in size as they mature. According to Blackburn, at birth there are 20-70 million alveoli and pre-alveolar air sacs; by 6 months, between 85% and 90% of alveoli are formed; and by 8 years the child's alveoli capacity has expanded to 300 million. In all of these stages, nutrients are critical for the growth and development of not just respiratory tissue, but also the bone, cartilage, and muscle tissue that will form the ribcage to house the lungs. This connection between bone growth and respiratory development will continue through childhood.

The substance called surfactant is a critical part of healthy respiratory function. It is a lipoprotein that is responsible for maintaining the gas exchange capacity of the lungs. It also plays a role as a pathogen barrier and inflammatory mediator in immune function.

We know that a healthy gut is critical for a healthy immune system in an infant. But immunity is hardly confined to the gut. One of the most obvious indicators parents can use to judge the overall immune health of a baby is the presence of respiratory infections. Respiratory illness is the leading cause of hospitalization among young children. And when it is severe enough to require hospitalization, respiratory illness can dramatically increase the risk of childhood asthma.

There are a number of factors, including nutriention, that are important in respiratory immunity. While vitamin D is most often associated with its role as a critical part of healthy bone growth, researchers know that it also plays a key part in the regulation of innate immunity. There is increasing evidence that pathways that involve the vitamin may be involved in several autoimmune diseases, from rheumatoid arthritis to possibly even multiple sclerosis, and that understanding these mechanisms may shed light on treatment possibilities.

Another group of nutrients that researchers believe are involved in respiratory immune health are the lipids known as LCPUFAs (long-chain polyunsaturated fatty acids). LCPUFAs are important structural and functional components of immune cells and have multiple roles, from regulating inflammation to signaling the production of specialized immune cells.