Vitamin D after 50 in NZ: deficiency, dosage, and the winter problem

If you feel flatter over winter — more tired, achier, quicker to catch whatever’s going around — vitamin D is something to consider. It’s a nutrient many New Zealanders may be quietly short on, and deficiency is increasingly common as we get older.

I’m Dr Roderick Mulgan, an Auckland GP and the founder of Lifeguard Health. This is a plain-English guide to vitamin D for adults 45 and over in New Zealand: why deficiency is common, how much you actually need, which form to choose, how to take it, and where a supplement fits.

The short version

For most adults, the body makes plenty of vitamin D from sunlight in the warmer months. The problem is that two things chip away at that supply: a New Zealand winter, when the sun sits too low to do the job, and getting older, when skin makes vitamin D less efficiently and we tend to spend more time indoors. That’s why a daily top-up over the cooler months is sensible for a lot of over-50s here — and why some people may benefit from it year-round.

Why New Zealand is a special case

Vitamin D is made in the skin when it’s hit by UVB rays from the sun. The catch is that UVB only reaches us strongly when the sun is high in the sky. Across most of New Zealand, from roughly May to August, the sun never climbs high enough during the day to let your skin make meaningful amounts — and the further south you live, the longer that window lasts. Wellington, Christchurch and Dunedin feel this more than Auckland, but no part of the country is immune to it.

On top of latitude, some groups are more likely to run low whatever the season:

• Adults over 50, because skin becomes less efficient at making vitamin D with age.
• People with naturally darker skin, which needs more sun to make the same amount.
• Anyone who covers up, works indoors, or doesn’t get outside much.
• People in residential care or with limited mobility.
• Those carrying more weight, as vitamin D gets held in body fat and is less available.

If that sounds like you, vitamin D is worth paying attention to. 

What vitamin D actually does

Vitamin D earns its keep in three areas that matter more, not less, as we age.

Bones. Its best-known job is helping your body absorb calcium, which is why it’s central to bone strength through midlife and beyond. Without enough vitamin D, even a good-calcium diet doesn’t fully land.

Muscles and balance. Vitamin D supports normal muscle function. For older adults that’s not just about strength — steady muscles mean steadier balance and more confidence on your feet.

Immune health. It plays a role in normal immune function, which is part of why low levels and winter coughs and colds so often travel together — exactly at the time of the year when NZ sun can’t top you up.

To be clear about what supplements can and can’t do: vitamin D supports bone, muscle and immune health. It isn’t a treatment for osteoporosis or any illness, and no supplement should be sold to you as one. If you have a diagnosed condition, that’s definitely a conversation you should be having with your GP.

D3 or D2 — which form to choose

You’ll see two forms on the shelf. Vitamin D3 (cholecalciferol) is the form your own skin makes and the one to look for — it raises and holds your blood level more effectively than vitamin D2 (ergocalciferol). D3 is usually derived from lanolin (sheep’s wool); vegan D3 from lichen is also available if that matters to you. Unless your GP has prescribed D2 for you for a specific reason, D3 is the sensible default option.

How much do you need?

For general health, many New Zealand adults do well on a modest daily top-up — commonly around 1000 IU (25 micrograms) — particularly through autumn and winter. People who are genuinely low, or in a higher-risk group, sometimes need more, but that’s where a blood test and your doctor come in rather than guesswork or general advice.

The important principle is that more is not better. Vitamin D is fat-soluble, so it builds up in the body, and very high doses taken long-term can cause problems. A steady, sensible daily amount is far better than occasional large hits. If you’re considering a high-dose product, please check with your GP or pharmacist first.

Vitamin D daily requirements by age (the actual numbers)

People often ask what their vitamin D3 daily requirements really are, so here are the figures. International guidelines — such as the US National Institutes of Health and the European Food Safety Authority — set general daily reference intakes along these lines:

Group	Reference intake (IU/day)	(micrograms/day)
Children (1–18 years)	600	15
Adults (19–70 years)	800	20
Adults (71 years and over)	1000	25
Pregnant or breastfeeding	800	20

Treat these as baselines for a general population, not a personalised prescription. In practice, many New Zealand adults — especially over 50 and through our low-sun autumn and winter — do well on around 1000 IU (25 micrograms) a day, which sits comfortably inside these ranges.

Vitamin D doesn’t work alone

Vitamin D is part of a team, and the rest of the team matters — especially for bones. Calcium is the raw material vitamin D helps you absorb, ideally from food (dairy, tinned fish with bones, leafy greens). Magnesium is needed to activate vitamin D, and many midlife adults run short on it. Vitamin K2 helps direct absorbed calcium into bone rather than soft tissue. You don’t need to overthink this — a varied diet plus a sensible daily foundation covers most people — but it’s why a single mega-dose of vitamin D in isolation is rarely the smart play.

How to take it

Two practical points make a real difference. First, take vitamin D with a meal that contains some fat — because it’s fat-soluble, this meaningfully improves absorption, so your morning capsule does best alongside breakfast rather than on an empty stomach. Second, daily beats sporadic: a small amount every day keeps your level steady far more reliably than a big dose now and then. Build it into a routine you won’t forget — same meal, same time.

Sun, food or supplement?

All three play a part, but each has limits here.

Sun is the body’s main source in summer — a little regular outdoor time, with sensible sun care, does the job from spring to autumn. In winter, NZ sun simply can’t make enough, no matter how long you’re out.

Food contributes a bit — oily fish, eggs and fortified foods — but it’s genuinely hard to get enough from diet alone, which is why food rarely closes a winter gap on its own.

A supplement is the reliable way to keep levels steady through the months when sun and food fall short. It’s the simplest and most practical option for most over-50s in New Zealand over winter.

How to know if you’re low

The tricky thing about low vitamin D is that the signs are vague and easy to put down to other things: tiredness, low mood, aching muscles or bones, and getting run-down more easily. None of these is proof on its own.

The only way to actually know is a blood test — a simple one called 25-hydroxyvitamin D, reported in nmol/L. Your GP interprets the number against your situation and advises whether to top up and by how much. It’s worth asking for one if you’re in a higher-risk group, if you’ve got persistent bone or muscle aches, or if you simply want your baseline before supplementing. If you do start a daily top-up, there’s rarely any need to retest constantly — a recheck after a few months, if your GP suggests it, is plenty.

If you’re over 45

A few things change with age. Bone density falls, so the cost of running low is higher, and postmenopausal women in particular may need a little more as hormonal changes speed up bone loss. Some medicines — including long-term steroids (glucocorticoids) and certain anti-seizure medications — can interfere with how the body handles vitamin D. If that’s you, it’s worth raising with your GP rather than guessing.

Safe upper limit. For healthy adults, the generally accepted long-term upper limit is about 4000 IU (100 micrograms) a day. Vitamin D toxicity is rare and comes from very high doses taken over a long period, not from sensible daily amounts — but it’s the reason “more is better” doesn’t apply here. If you’re considering anything near that level, check with your GP or pharmacist first.

If a test shows you’re low, the usual approach is a daily top-up — sometimes a higher dose to begin with, then a steady maintenance amount — alongside sensible sun and vitamin‑D‑rich foods such as oily fish and eggs. Most people see their blood levels improve within about two to three months, and a recheck then (if your GP suggests it) confirms you’re on track.

When to be a bit more careful

Vitamin D is very safe at sensible daily doses, but a few people should check with their GP before taking it — particularly at higher doses. That includes anyone with a history of kidney stones or kidney disease, high blood calcium, conditions such as sarcoidosis, or those on certain heart medications. Taken in very high amounts over a long period, vitamin D can push blood calcium too high, which causes nausea, excessive thirst and other problems. This isn’t a reason to avoid it — it’s a reason to stick to a sensible daily amount rather than self-prescribing higher doses.

Where Lifeguard fits

I include vitamin D in Lifeguard Immune, our doctor-formulated winter immune formula — and that pairing is deliberate, because vitamin D and immune resilience work closely together, especially through a New Zealand winter. Alongside vitamin D3, Immune also brings vitamin C, copper, zinc, selenium, elderberry, andrographis and quercetin in a daily capsule formula.

It’s NZ-made, formulated by me, and backed by our 60-day satisfaction guarantee with free NZ shipping over $95. If you’d rather cover your full daily foundation, Lifeguard Essentials contains several key plant extracts which support healthy immune function in middle age and beyond, and the Lifeguard Bundle brings Essentials, Immune and Sleep together. You can also read our healthy ageing supplements guide. 

A supplement supports good nutrition and healthy lifestyle choices — it isn’t a substitute for medical care. If you think you may be deficient, ask your GP for a blood test.

Frequently asked questions

How much vitamin D should I take over 50 in NZ?

Many New Zealand adults do well on a modest daily top-up — commonly around 1000 IU (25 micrograms) — especially through autumn and winter. If you’re genuinely low or in a higher-risk group you may need more, but that should be guided by a blood test and your GP rather than guesswork. More is not better, as vitamin D builds up in the body.

Should I take vitamin D3 or D2?

Vitamin D3 (cholecalciferol) is the form to look for — it raises and holds your blood level more effectively than D2 (ergocalciferol), and it’s the same form your skin makes from sunlight. Vegan D3 from lichen is available if you prefer. Use D3 unless your GP has specifically prescribed D2.

Is vitamin D deficiency common in New Zealand?

Yes, more than many people expect. Our southern latitude means winter sun can’t make meaningful vitamin D from about May to August, and the risk rises with age, darker skin, covered skin and time spent indoors. It’s one of the most common nutritional shortfalls we see here.

Should I take vitamin D in winter?

For many over-50s in New Zealand, a daily top-up through the cooler months is sensible, because sun and diet rarely cover the gap then. If you’re unsure, a blood test will tell you where you stand.

When is the best time to take vitamin D?

With a meal that contains some fat — vitamin D is fat-soluble, so taking it alongside food improves absorption. Breakfast is an easy anchor. A small daily dose keeps your level steadier than an occasional large one.

Can you take too much vitamin D?

Yes, at very high doses taken long-term, because it builds up in the body and can raise blood calcium too high. Sensible daily amounts are very safe. If you have kidney problems, high blood calcium or conditions such as sarcoidosis, check with your GP prior to supplementing.

Can I get enough vitamin D from the sun in NZ?

In spring, summer and early autumn, usually yes — a little regular outdoor time with sensible sun care does the job. In winter, no: across most of New Zealand the sun sits too low to let your skin make enough, however long you’re outside.

What are the signs of low vitamin D?

They’re vague — tiredness, low mood, aching muscles or bones, and getting run-down more easily — and these overlap with plenty of other things. That’s why a blood test, rather than symptoms alone, is the way to know.

Written by Dr Roderick Mulgan, NZ GP and founder of Lifeguard Health. This article is general information, not medical advice. For advice about your own vitamin D level or dosing, see your GP.