Vitamin D is sometimes called the “sunshine vitamin.”

Unlike many other vitamins, we can obtain vitamin D not only through food. Our skin can also produce it when exposed to UVB radiation from sunlight.

One of vitamin D’s clearest and most important roles is to help the body absorb calcium and support healthy bones and muscles.

For women over 40, this becomes particularly relevant. Bone mass gradually declines with age, and bone loss can accelerate after menopause as oestrogen levels fall. If vitamin D levels are also persistently low, bone health may come under additional pressure.

Can you be vitamin D deficient without knowing it?

Yes.

Many people with low vitamin D levels have no obvious symptoms.

Some people may experience:

  • tiredness
  • muscle weakness
  • mild bone discomfort

However, these symptoms are non-specific. Feeling tired or weak does not necessarily mean you have vitamin D deficiency.

Whether testing is appropriate usually depends on your individual risk factors, medical history and clinical circumstances.

What are the main risks of long-term vitamin D deficiency?

1. Bone loss and osteoporosis

Vitamin D helps the body absorb calcium.

When vitamin D deficiency is severe or prolonged, normal bone mineralisation can be affected. In adults, severe deficiency can contribute to osteomalacia, and low vitamin D can also be associated with poorer bone health.

For women approaching or going through menopause, this matters because falling oestrogen levels already contribute to faster bone loss.

2. Muscle weakness, falls and fractures

Vitamin D also contributes to normal muscle function.

In older adults, vitamin D deficiency may be associated with muscle weakness and a greater risk of falls and fractures.

For ageing parents, vitamin D therefore may need to be considered as part of a broader assessment of bone health, strength and falls risk.

3. Severe deficiency in children can cause rickets

In babies and children, prolonged severe vitamin D deficiency can lead to rickets, which affects developing bones.

Who is more likely to develop vitamin D deficiency?

Risk may be higher in people who:

  • spend very little time outdoors
  • remain indoors for long periods
  • live in hospital, rehabilitation or residential aged care settings
  • regularly cover most of their skin with clothing
  • have naturally darker skin
  • have certain conditions that reduce fat absorption, such as Crohn’s disease
  • have advanced kidney disease
  • are pregnant or breastfeeding
  • take certain medicines or have conditions that affect vitamin D metabolism

Season and lifestyle can also make a difference. People who spend less time outdoors during winter may be at greater risk of low vitamin D.

How should we maintain or improve vitamin D levels?

A useful way to think about vitamin D is in three layers:

sunlight → food → supplements when needed

rather than immediately asking, “How many IU should I take?”

1. Get sunlight safely

In Australia, sunlight is the main source of vitamin D for most people.

But that does not mean we should deliberately spend long periods in the sun to increase vitamin D.

When the UV Index is 3 or above, sun protection remains important because excessive UV exposure increases the risk of skin cancer.

More sun exposure does not continue to increase vitamin D indefinitely.

A better principle is:

Vitamin D matters, but it should not come at the cost of unnecessary UV exposure and skin cancer risk.

If you are concerned about vitamin D deficiency, speak with your GP rather than simply increasing your time in the sun.

2. Include dietary sources of vitamin D

Foods that can provide some vitamin D include:

  • oily fish
  • eggs
  • some fortified milks
  • other vitamin D–fortified foods

However, food alone may not provide enough vitamin D for everyone, which is why sunlight remains an important source for many Australians.

3. Use supplements when they are actually needed

If a blood test confirms low vitamin D, your doctor may recommend a supplement.

One important distinction is:

Nutrient reference intakes are not the same as treatment doses

Australian and New Zealand Nutrient Reference Values list an Adequate Intake for vitamin D of approximately:

  • 19–50 years: 5 micrograms per day
  • 51–70 years: 10 micrograms per day
  • over 70 years: 15 micrograms per day

This is approximately:

  • 200 IU
  • 400 IU
  • 600 IU

These figures are population-level nutrient reference values for generally healthy people. They are not instructions for treating an established vitamin D deficiency.

If someone is deficient, the dose and duration of supplementation may depend on:

  • blood vitamin D levels
  • age
  • medical conditions
  • kidney function
  • absorption
  • medicines
  • individual risk factors

For that reason, it is better not to assume that taking a higher dose for longer is automatically better.

Can you take too much vitamin D?

Yes.

Vitamin D is a fat-soluble vitamin. Excessive supplementation over time can lead to vitamin D toxicity and high calcium levels in the blood.

So supplements should still follow a simple sequence:

Do I need it? → Why am I low? → How much do I need? → For how long? → Do I need follow-up?

rather than:

“Vitamin D is good for me, so more must be better.”

When should you discuss vitamin D with your GP?

It may be worth discussing vitamin D with your GP if you:

  • rarely spend time outdoors
  • spend long periods indoors
  • have darker skin
  • regularly cover most of your skin
  • have osteoporosis or increased fracture risk
  • are older and at increased risk of falls
  • have a condition that affects nutrient absorption
  • have kidney disease
  • have other risk factors identified by your healthcare professional

If appropriate, your GP can arrange a blood test and advise whether supplementation is necessary.

Liora takeaway

There are four useful things to remember about vitamin D:

First, vitamin D is particularly important for calcium absorption, bone health and muscle function.

Second, deficiency may not cause obvious symptoms.

Third, in Australia, do not overexpose yourself to UV radiation simply to increase vitamin D.

Fourth, supplements are not automatically better at higher doses. If you are deficient, the right dose depends on your individual situation.

For women over 40, vitamin D is worth considering as part of overall bone-health planning, but it is only one piece of the picture.

Calcium intake, resistance training, weight-bearing activity, smoking, alcohol intake and osteoporosis risk assessment after menopause are also important.