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Many hormones play a significant role in the body. As we age, hormonal changes can affect us in many ways. You will come across a number of them in this book – here is an overview of the most important ones.

Human growth hormone: secreted in much greater amounts in youth to help bones grow. Also helps the body to metabolize fats. Levels tend to diminish with age, which is thought to contribute to decreases in cell membrane composition.

Progesterone: the gestational hormone, which prepares the lining of the uterus for the fertilized egg and maintains pregnancy. Progesterone is a ‘precursor’ hormone, which can be converted by the body into other steroid hormones. As levels fall, an imbalance occurs between this hormone and the other primary female sex hormone, oestrogen. This is linked with weight gain, decreases in bone density and a possible reduction in sex drive.

Testosterone: the male sex hormone, most commonly known for promoting libido and stimulating sperm production. Also helps protein build muscles, skin and bone, and nourishes all the tissues of the male urinary and reproductive systems. Regulates the production of prostaglandin, which seems to keep prostate growth under control. In both sexes, testosterone levels decrease with age. This has a significant impact on health and wellbeing, contributing to decreases in bone and muscle development as well as reduced virility. Recent evidence has linked low testosterone with Alzheimer’s disease.

DHEA: dubbed the ‘mother of all hormones’ because the body uses it to produce a number of hormones including testosterone, oestrogen and progesterone. DHEA production drops sharply after the age of 25; by the age of 75 we are producing only 10–20 per cent of the DHEA our bodies manufactured at 20, and this has an impact on the other sex hormones.

Thyroid hormones: regulate the body’s metabolism, temperature and heart rate. If the thyroid isn’t functioning at its optimal level, neither are you. Thyroid deficiency is not specifically age-related as woman can be prone to it at all ages, especially during and after pregnancy.

Insulin: the main hormone for promoting the transport of glucose rather than fat into muscle cells to be used as energy; also a potent inhibitor of the fat-stimulating hormone HSL. Excess body fat is associated with insulin resistance. Some researchers have suggested that reducing body fat through calorie restriction without under-nutrition may help improve the insulin response, which can reduce risk factors for disease. You can enhance your insulin sensitivity by increasing your intake of the healthy omega-3 fatty acids found in oily fish such as salmon, mackerel and fresh tuna, and in walnuts, flaxseeds and soya products. Vigorous exercise can also improve insulin sensitivity.

Epinephrine and cortisol: prepare the body for an instant state of readiness – the classic ‘fight or flight’ response. Epinephrine is the primary hormone that stimulates lipolysis, the breakdown of fat. Epinephrine binds to the receptors on various cells and can either activate or inhibit HSL, the hormone responsible for fat mobilization. Epinephrine excretion appears not to change with age. Cortisol releases glucose and fatty acids into the bloodstream to provide energy to the muscles. It also has a direct impact on the body’s blood sugar levels. If too little cortisol is released, hypoglycaemia (low blood sugar) can develop; if too much cortisol is released, hyperglycaemia (high blood sugar) can develop, which can increase the risk of developing diabetes. When people experience prolonged stress, cortisol levels remain elevated for long periods, and recent research shows that this can lead to weight gain, especially on the belly. Cortisol excretion appears to increase with age.