Around 18% of UK adults and 19 to 23% of Australian adults are vitamin D deficient, and those figures climb to about 31 to 36% over winter.

New Zealand likely sits somewhere similar. And it's not only deficiency to watch for: insufficiency, a lower-grade shortfall, is common and easily missed.

Why women are at risk

Your skin makes most of your vitamin D from sunlight, and food provides only a little, which makes late winter and early spring the danger zone. Some women are at even higher risk:

  • Those who spend most of the daylight hours indoors

  • Those who cover most of their skin outdoors or use sun protection consistently (which is important for skin cancer prevention)

  • Those living in the southern parts of the country through winter

  • Those who are pregnant or breastfeeding, as your baby draws on your stores

Sufficient, insufficient or deficient? Making sense of your results

Vitamin D is measured as 25-hydroxyvitamin D in a blood test. Here's a simple way to think about it:

  • Sufficient: 50 nmol/L or above. Your levels are healthy.

  • Insufficient: about 25 to 49 nmol/L. Not full deficiency, but short of where you want to be, and often without obvious symptoms.

  • Deficient: below about 25 to 30 nmol/L (the cut-off varies slightly between NZ and Australian sources). This needs your GP's input.

A test at the end of winter shows where you're most likely to bottom out.

Know the signs

Low vitamin D is often silent. When it does show, look for tiredness, bone or muscle aches, low mood and getting sick more often.

How much do you need?

Under the Australian and NZ Nutrient Reference Values (an Adequate Intake):

  • Reproductive-age women: 5 µg (200 IU) per day

  • Pregnancy: 5 µg (200 IU) per day

  • Breastfeeding: 5 µg (200 IU) per day

  • Upper limit: 80 µg (3200 IU) per day

Why doesn't the requirement change? The official reference value stays the same across these life stages, but your baby relies on your stores, so knowing your own level matters more than the headline number.

Should you supplement?

Late winter to early spring is when a supplement is most worth considering. Around 1000 IU (25 µg) daily, taken consistently, is often effective at lifting levels, ideally after a blood test confirms where you sit. Vitamin D is fat soluble, so take it with a meal that contains some fat to improve absorption. It also helps your body absorb calcium, so the two work as a pair.

What about sunshine? About 15 minutes of direct sun on bare skin is often recommended, but with skin cancer risk and New Zealand's high UV, it's a bit of a catch-22. Check the daily UV index and follow sun-safe advice, and rely on food and supplements too.

Food first: build a vitamin D-smart plate

Food provides only a small amount, but it all counts. Good sources are oily fish (salmon, mackerel, sardines), egg yolks, fortified milks and cereals, and UV-exposed mushrooms. Fun fact: mushrooms left in the sun absorb UV light, which increases their vitamin D content.

Try these pairings:

  • Grilled salmon with avocado: a naturally vitamin D-rich fish with a fatty partner for maximal absorption in one sitting.

  • UV-exposed mushroom and egg scramble cooked in olive oil: cooking in fat improves uptake.

  • Fortified cereal with fortified milk and a handful of almonds: vitamin D and calcium together, with a little fat.

The takeaway

Don't guess. Ask your GP for a vitamin D test at the end of winter, especially if you're planning a pregnancy, and discuss a daily supplement if your levels are low.