The role of stress in illness, including reference to immunosuppression…

The idea

The link is not magic; it is cortisol. Sustained cortisol reduces lymphocyte production and blunts natural killer cell activity, so infections take hold. Kiecolt-Glaser took blood from seventy-five medical students a month before exams and again during them: natural killer activity fell in the exam sample, furthest in students also reporting loneliness. Her wound-healing work found biopsy wounds in carers of relatives with Alzheimer's took roughly nine days longer to close than in matched controls. On the heart, repeated adrenaline surges raise blood pressure and scour artery walls, encouraging plaque and clotting; Williams found the angriest of thirteen thousand adults were about two and a half times likelier to have a heart attack. All of it is correlational, and stressed people also smoke and sleep badly.

What earns the marks

• The mechanism first: chronic cortisol suppresses immune function, reducing lymphocyte numbers and natural killer cell activity.
• Kiecolt-Glaser's medical students, with the direction of the finding stated: natural killer cell activity was lower during exams than a month before.
• The wound-healing study on carers, where healing took around a quarter longer than in controls.
• The cardiovascular mechanism: raised blood pressure and heart rate, damage to artery linings, plaque formation and increased clotting.
• Cohen's common cold study, where a higher proportion of the high-stress group developed colds after controlled exposure to the virus.
• AO3: the evidence is correlational, so illness could precede or cause the stress rather than follow it.
• AO3: the indirect behavioural route, since stressed people smoke, drink, sleep less and eat worse, which confounds the direct immune explanation.

Common mistakes and how to put them right

• Writing that stress causes illness when the studies are correlational or quasi-experimental and cannot show causation.

• Claiming stress always weakens immunity.

  Put it right: Brief acute stressors can temporarily boost immune activity, so the relationship is not a straight line.

• Naming Kiecolt-Glaser without saying which way the result went, which earns no credit for the finding.

• Treating immunosuppression as just meaning catching colds, instead of a measurable change in immune cells.

• Explaining cardiovascular damage as stress hormones being toxic, rather than through blood pressure, vessel damage and clotting.

Exam tips

• Use the figures. A stated percentage or a stated number of days is credited where a vague claim that more people got ill is not.
• Application items put a character under a deadline or in a caring role, so name the measure and the study that fits that scenario.
• For evaluation, the third-variable lifestyle confound and the difficulty of measuring immune function are the two strongest lines available.