Dr Phillips’ own work has shown that as we age, our immune system becomes less efficient, and stress can worsen this. The adrenal glands produce the stress hormone cortisol – an immune suppressor long prescribed as corticosteroids (steroids) to reduce inflammation. The adrenals also produce dehydroepiandrosterone (DHEA) which counters the negative effects of cortisol and helps to increase immune function. After the age of about 30, levels of DHEA drop until, by the time we are 70 or 80, they have fallen to about ten per cent of their peak output, leaving older adults with a higher cortisol:DHEA ratio, thus reducing immune function and leaving them open to infections.