You'd be forgiven for thinking that living in Australia means you're getting enough vitamin D all year round. After all, we're known for our sunshine.
But winter tells a different story.
As the days get shorter and cooler, many of us spend less time outdoors, cover more of our skin with clothing, and only see daylight during the commute to and from work. Even though the sun is still shining, these seasonal changes can make it harder for your body to produce enough vitamin D.
The main reason is that your skin needs UVB rays from sunlight to make vitamin D. During winter, there is generally less UVB available, particularly in southern parts of Australia, and many daily routines simply don't provide enough meaningful sun exposure.
While not everyone will develop low vitamin D during winter, it's a time of year when levels commonly decline. Understanding why can help you make informed decisions about your sun exposure, lifestyle, and whether it's worth speaking to your healthcare professional.
Why winter can affect your vitamin D levels
Winter changes more than just the temperature. It changes how much sunlight reaches your skin and how much time most of us actually spend outside.
Think about a typical weekday. You leave home before the sun is fully up, drive or catch public transport to work, spend most of the day indoors, then head home as it's getting dark. On weekends, colder weather often means staying inside rather than spending hours outdoors.
None of those habits are unusual. But together, they can reduce the amount of UVB your skin receives, making it more difficult for your body to produce vitamin D.
For broader context, see Vitamin D: The Overlooked Essential Vitamin for Women’s Health.
It's UVB (not just sunshine) that matters
Many people assume that if it's bright outside, they're making vitamin D.
Not necessarily.
Your body produces vitamin D3 when UVB rays reach your skin. That vitamin D is then converted in the liver to 25-hydroxyvitamin D, the form measured in blood tests to assess your vitamin D status.
The important point is that being outdoors only helps if enough UVB reaches enough exposed skin. Sitting beside a sunny window doesn't have the same effect because glass blocks most UVB radiation.
Why winter sun isn't the same as summer sun
In winter, the sun sits lower in the sky. That means sunlight travels through more of the Earth's atmosphere before it reaches you, reducing the amount of UVB available for vitamin D production.
Winter days are also shorter, giving you fewer opportunities to be outside during the middle of the day when UVB is generally strongest.
This is why a bright, sunny winter's day doesn't necessarily mean you're producing enough vitamin D. Sunshine and vitamin D-producing UVB aren't the same thing.
Winter habits can make vitamin D even harder to produce
Seasonal routines can further reduce your vitamin D production.
During winter, many people wear long sleeves, jackets, scarves and long pants, leaving less skin exposed to sunlight. Others spend most of their day indoors at work, in shopping centres, at home, or commuting by car or public transport.
Consistent sunscreen use can also reduce the amount of UVB reaching the skin, although its effect varies depending on how much is applied and how consistently it's used.
Learning more about vitamin D support options
If you are exploring support options when sun exposure is limited, Vitamin D and Vitamin D3 - Vegan each provide 25 micrograms of vitamin D3, which is 1000 IU per dose.
Some people take vitamin D with a meal because it is a fat-soluble vitamin. If you want more context on supplement absorption, read What Is Bioavailability.
If bone health is part of the picture, Calcium Plus D3 is another relevant option because vitamin D supports calcium absorption. You can also explore How Vitamin D Can Help Improve Your Bone Health and Vitamin D and Immunity: What You Need to Know for broader reading.
Frequently Asked Questions
Can you become vitamin D deficient in Australia during winter?
Yes. Vitamin D can drop during an Australian winter because UVB exposure often falls with shorter days, lower sun angle, more indoor time, and heavier clothing coverage.
Why do vitamin D levels drop in winter?
Vitamin D levels tend to fall after periods of reduced sun exposure. In winter, there is usually less UVB available for skin production, and many people spend less time outdoors during useful daylight hours.
Does sunny weather mean you are getting enough vitamin D?
No. Bright or mild weather does not automatically mean enough UVB is reaching your skin. Visible sunshine and vitamin D-producing exposure are not the same thing.
Who is more at risk of low vitamin D in Australia?
Risk is higher in people who spend most daylight hours indoors, live in southern areas, have darker skin, cover more of their skin, or are older. The chance increases when several of these factors overlap.
References
- National Institutes of Health Office of Dietary Supplements. Vitamin D Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
- Cancer Council Australia. Position statement: Sun exposure and vitamin D. https://www.cancer.org.au/health-professionals/position-statements/sun-exposure-and-vitamin-d
- Better Health Channel. Vitamin D. State Government of Victoria. https://www.betterhealth.vic.gov.au/health/healthyliving/vitamin-d
- Holick MF. Vitamin D deficiency. New England Journal of Medicine. 2007;357(3):266-281.
This is general information only and not medical advice.
