Winter respiratory infection rates rise predictably with the reduction in UVB radiation that occurs from October in northern latitudes. Vitamin D synthesis ceases, and the immune impairment from deficiency becomes progressively apparent across the winter months. Simultaneously, the fruit and vegetable diversity that characterises summer diets contracts as seasonal variety narrows. The adults who enter winter with the best immune resilience are those who used summer and autumn to build it.
The Three Autumn Priorities
- Vitamin D status: check serum 25-hydroxyvitamin D in October; supplement at 1,000 to 2,000 IU daily from September onwards; do not wait for deficiency symptoms which lag behind the blood level change by weeks to months
- Gut microbiome diversity: increase plant food variety to at least 30 different species per week through autumn; the microbiome diversity built in autumn persists through winter even as dietary variety narrows
- Dietary antioxidant capacity: prioritise seasonal autumn foods including squash, apples, pears, root vegetables, and dark leafy greens that provide beta-carotene, vitamin C, and polyphenols
Fermented Food Emphasis in Autumn
Autumn is traditionally the season of fermented food preparation: sauerkraut from autumn cabbage, kimchi from late-season vegetables, and kefir from milk. These fermented foods support gut microbiome diversity and immune function through the winter. Increasing fermented food consumption from September through November measurably improves immune marker profiles by December in adults who were not previously consuming them regularly.