When is Thin Too Thin?

Leptin is a crucial metabolic regulator of energy sufficiency and control of proper reproductive function. Women of insufficient BMI (body mass index) often may have a cessation of their menstrual cycle, and subsequently, suppression of the reproductive access. This type of menstrual irregularity is attributed to the diagnosis of hypothalamic amenorrhea. When is thin too thin? Although many illnesses can cause hypothalamic amenorrhea; it is most notably associated with extreme weight loss and exercise. The body can interpret these lifestyle choices as negative stressors.

When a select group of women who demonstrate hypothalamic amenorrhea are exposed to leptin, their menstrual cycles return. Hormone cycles are normal, they are able to grow dominant follicles within the ovaries, ovulate them and become pregnant. Therefore, leptin plays a pivotal role in maintaining reproductive health and regulating menstrual cycles.

Leptin also plays a permissive role in the onset of puberty, an incredibly energy-demanding process! For male and females alike, time of puberty initiation is correlated with body size (and body fat). Prior to pubertal onset, both mice and primates (us) alike demonstrate nocturnal surges of the hormone.

The writing is on the proverbial wall. From birth, there already exists a discrepancy in leptin levels between the sexes. Newborn females have higher leptin levels in the umbilical cord blood. These higher levels are sustained through childhood, puberty and into the reproductive years. The clear correlation between leptin and BMI implicates higher leptin levels with adipocity. Leptin is most certainly part of this chain and is required, but it is not the sole factor. It plays an instrumental part in a signaling cascade.