Meet Your Hormones: Discover the Hidden World of the Chemical Messengers in Your Body

Egyptian "Mummies"

One of the earliest written records of hormone action — a urine-based pregnancy test — has been found on a papyrus of 1350 BC. Egyptian women would moisten a sample of barley or wheat seeds with urine over the course of several days. If no seeds germinated, the woman was not pregnant. If barley seeds grew, she was carrying a boy; if wheat seeds grew, a girl. In 1963 the test was shown to detect raised levels of estrogens with a 70 percent success rate. Its accuracy in predicting gender, however, is not recorded...

Melatonin

Commonly known as the sleep hormone, melatonin is closely involved in determining our sleep/wake cycles. Produced by the pineal gland, melatonin signals to the brain that it is time to sleep. Ideally the levels of the stress hormone cortisol dip as the day goes on. This allows the effects of melatonin to take over, making us feel sleepy as the day draws to an end. As dawn breaks cortisol levels peak — waking us up, boosting our energy levels and turning on our appetite.

Tryptophan

Tryptophan is one of the essential amino acids, used by the body to make proteins. It is a key building block of the sleep hormone melatonin (and the feel-good hormone serotonin, page 111), so ensuring your diet contains plenty of tryptophan will encourage sleep. Turkey has something of a reputation as a sleep-inducing food, but other sources of tryptophan such as cheese, soybeans, cod and dried spirulina — a seaweed — have higher quantities. Many fruits and vegetables also contain tryptophan, with bananas a well-known example.

Bone Density

Bone is adversely affected by the decline in levels of Vitamin D as you age; a reduced skin response to UV light results in a decrease in its production of up to 50 percent. The effect is compounded in postmenopausal women as their estrogen levels tail off (page 89), which further affects bone. The result is a higher incidence of osteoporosis (weakening bone density) and associated fractures, compared to men. Men are partly protected by their natural higher peak bone mass (bones achieve maximum density in both sexes around age 30). Although the dominant male sex hormone testosterone declines gradually with age, its protective effects on bone are far less significant than estrogen its equivalent, in women.

Jet Lag and Shift Work

Our jet-setting ways can now propel us into different time zones faster than our bodies are able to adjust, leaving us with jet lag. If your body were to release cortisol in the morning, preparing you for the day ahead, only in response to increasing daylight, you would not experience jet lag. However, you might arrive at work late during the short daylight hours of winter. Skew your body clock by jetting into a time zone several hours earlier, and your body will release cortisol while you are trying to sleep.

People who do shift work also experience symptoms similar to those of jet lag: being hungry, tired and awake at the wrong times. If someone were to work night shifts constantly, their body would eventually adjust so that they had an increase in cortisol levels in the late afternoon, for example. However, constant changes in the times of work shifts — between day, twilight and night — mean that the body has a hard time establishing rhythmic patterns.

Do Boys Grow Breasts if They Consume Too Much Soy?

There is no evidence to suggest this is the case. Soy contains plant estrogens known as isoflavones, which are structurally very similar to the primary estrogen hormone in humans, 17-B-estradiol. Because isoflavones have a similar structure to estrogen, they can bind with estrogen receptors and trigger effects in the target cells. Concerns have therefore been raised that a diet rich in isoflavones may trigger early puberty in girls and lead to "feminizing" effects in boys. Recent reviews of studies published over the last 20 years have found no evidence to substantiate this. However, there does seem to be evidence that isoflavones may have a protective effect against cancer and many chronic diseases, including diabetes and cardiovascular disease. Studies are ongoing, but at the moment the evidence suggests that the benefits of eating a diet rich in isoflavones outweigh any potential costs.