Tim Spector: Why He Changed His Mind About Vitamin D and Sunlight

Tim Spector, professor of epidemiology at King's College London and ZOE's scientific co-founder, sits down with Jonathan Wolf for an annual stock-take of what he now believes differently. He opens with why nutrition science moves so slowly: government guidelines are forced into black-and-white language, industry lobbies against change, and even doctors are slow to abandon habits — the fat reversal took roughly a decade after the evidence became overwhelming. He then lays out his personal evidence ladder, from test-tube studies he ignores through to randomised trials and meta-analyses he acts on.

Vitamin D is his own cautionary tale: he promoted it for osteoporosis for years until large placebo-controlled trials showed no difference in fracture rates. What has not changed is his conviction about the gut microbiome and his view that ultra-processed foods are now the leading public health danger.

Then come the seven shifts: optimal flossing and its link to dementia risk, an above-average microplastics reading in his blood, a low omega-3 index he raised with anchovies and sardines instead of capsules, lifelong low B12 and folate he now supplements, a partial rehabilitation of vitamin D and a much warmer view of winter sunlight, a move from pure cardio toward mixed training with light weights and Pilates, and a serious upgrade to sleep quality including a two-hour eating cut-off and mouth taping. Creatine he tried and dropped — a 1.7% average gain was not worth it to him. The closing message is about method rather than any single nutrient: keep an open mind, get tested, and prefer whole foods and natural processes where a credible alternative exists.

• 1

  Floss until the bleeding stops 26:30

  Bleeding at the back of the mouth signals inflammation, not a reason to stop. Keep going daily with floss or interdental picks until the bleeding disappears.

• 2

  Make the easy plastic swaps 31:00

  Metal water bottle instead of plastic, glass where practical, a decent water filter, less packaged food, and a check on plastics in toothpaste and shampoo.

• 3

  Reach for oily fish before capsules 37:30

  Weekly anchovies, sardines, salmon, mackerel or herring lifted his omega-3 index from low to above average without a supplement — and brings nutrients a capsule doesn't.

• 4

  Test before you supplement B12 and folate 41:00

  Leafy greens cover folate for most people, and excess may cause its own problems, so a blood test comes first. Where levels really are low, both matter for nerves, blood and — in newer work — cognition in older adults.

• 5

  Get winter light on your skin 45:00

  Winter is when to seek sun rather than block it, while still avoiding burning. Mushrooms left on a sunny windowsill and oily fish add dietary vitamin D.

• 6

  Add two or three short weight sessions 48:30

  Twenty to thirty minutes with light weights, two or three times a week, alongside the cycling and swimming — and pick formats you actually enjoy so the habit survives.

• 7

  Stop eating two hours before bed 50:30

  Digestion keeps the body out of sleep mode, so he closes the kitchen two hours before bed, goes down half an hour earlier, and uses blackout curtains and soft earplugs.