Every August I have the same conversation two or three times a week. Someone sits down, mentions they've been tired and achy since the weather turned, and asks whether they should be taking vitamin D. It's a good question — and in southern Australia, winter genuinely does change the answer. Here's what the guidelines say, without the supplement-aisle hype.
Why winter is different down here
Most of our vitamin D isn't made from food. It's made in the skin, from UVB radiation in sunlight — and there simply isn't much of it about in a Melbourne winter. Cancer Council Australia frames it by the UV index: when UV is 3 or above, most people top up their levels just by spending a few minutes outdoors on most days. But in late autumn and winter in southern Australia the UV drops below 3, and at that point the advice actually flips. Sun protection is no longer needed, and the recommendation becomes to spend time outdoors in the middle of the day with some skin uncovered.
That's the opposite of what we're all trained to do the rest of the year, which is exactly why it catches people out.
How much sun, roughly
Healthy Bones Australia puts rough numbers on it for southern parts of the country. In summer, around 10–20 minutes between 10am and 3pm, four times a week, with about 10% of the skin uncovered — that's a face, hands and forearms. In winter, the same organisation suggests an hour or more around midday, four times a week, with a similar amount of skin exposed. They also note plainly that in southern areas, a supplement may be needed over winter regardless.
Treat those as a guide, not a prescription. Skin tone, cloud cover, how much you're actually uncovering and how much of your day happens indoors all move the number. And one line from Cancer Council is worth keeping front of mind: overexposure to UV is never recommended, even if you have a vitamin D deficiency. A winter walk with your sleeves pushed up is the goal — not a deliberate session in the sun.
Food helps, but it won't do the job alone
Healthy Bones Australia is blunt about this: food does not provide an adequate amount of vitamin D. The best dietary sources are oily fish — salmon, tuna, mackerel, herring — along with egg yolks, liver and fortified products such as some milks and margarines.
None of that is a reason to skip them. Oily fish twice a week earns its place on your plate for plenty of other reasons. Just don't expect a salmon fillet to correct a low blood level.
Who is most likely to run low
Some people start winter with much less in reserve. Cancer Council lists higher risk for people who are mainly indoors because of health or work, people with naturally darker skin, those who cover their skin for cultural or religious reasons, people avoiding the sun on medical advice, older adults who are housebound or in residential care, people carrying more body weight, infants of mothers who are deficient, and people on certain medications. Pregnancy and breastfeeding also raise the stakes.
If two or three of those describe you, winter is a reasonable time to ask your GP for a blood test rather than guessing.
What about a supplement?
Healthy Bones Australia recommends aiming for a vitamin D level of at least 50 nmol/L across the year. The doses they set out are modest: around 600 IU a day for adults getting some sun exposure, 800 IU from age 70, and 1,000–2,000 IU a day for people who genuinely avoid the sun. For a diagnosed moderate to severe deficiency they describe a higher short course of 3,000–4,000 IU for six to twelve weeks, followed by ongoing maintenance.
Those are guideline figures, not a self-prescription. Vitamin D is fat-soluble, so more is not better, and the sensible sequence is a blood test first, then a dose your doctor is happy with, then a recheck.
What I'd actually do this week
Nothing dramatic. Move your walk to the middle of the day rather than after dark, and push your sleeves up while you're out. Put oily fish on the shopping list twice. And if you tick one of the higher-risk boxes above, book the test instead of buying the biggest bottle on the shelf — knowing your number turns this from guesswork into a decision.
This article is for general information and isn't a substitute for individualised advice from your own doctor or dietitian.
Merve Tığlı, Dietitian
Sources: Cancer Council Australia — Vitamin D (sun safety); Healthy Bones Australia — Vitamin D and Bone Health fact sheet, 2nd edition (2024).