Vitamin D Deficiency: Symptoms, Causes, Tests and How to Prevent It

Long hours indoors, little time in the sun and a diet thin on the few foods that carry it have made vitamin D shortfall common. The difficulty is that the early signs are so ordinary — tiredness, a dull ache — that most people put them down to a busy week.

It is not only a bone issue either. Vitamin D is tied up with muscle function and immunity as well.

What is vitamin D?

Vitamin D is a fat-soluble vitamin, which means the body can store it. It is often called the sunshine vitamin because skin makes it when sunlight falls on it. Very few foods carry meaningful amounts, which is why sunlight matters so much.

What it does in the body

• Helps the gut absorb calcium and phosphorus
• Keeps bones and teeth strong
• Supports muscle strength and balance
• Plays a part in immune function

That spread is why a shortfall shows up in several places at once rather than in one obvious way.

Symptoms of a deficiency

Many people have no clear symptoms at first. When symptoms do appear, they tend to look like this:

• Tiredness and weakness that does not lift
• A low, persistent ache in the lower back, hips or legs
• Muscle weakness or cramps
• Finding stairs, or getting up from a chair, harder than it used to be
• Catching colds more often than usual
• More hair fall than normal
• A flat or low mood

None of this is specific to vitamin D. Anaemia, thyroid problems and simple sleep debt cause the same picture, so a blood test is worth more than self-diagnosis from a symptom list.

Why it happens

• Very little time outdoors — whole days spent inside a home or office
• Most of the skin kept covered
• Darker skin, which needs longer sun exposure to make the same amount
• A diet with little milk, curd, egg or fish
• Older age, when the skin makes less of it
• Some digestive conditions that interfere with absorbing fat

Who tends to be affected

Indoor workers, older adults, women who spend little time outdoors and anyone on a very restricted diet are the groups where a shortfall turns up most. In cities, tall buildings and haze cut down the usable sunlight as well.

The test and its ranges

The blood test is called 25-hydroxy vitamin D. Results are usually reported in ng/mL.

Laboratories differ slightly, so read the range printed on your own report. What the number means depends on your age, symptoms and other conditions — which is what the consultation is for.

Food sources

• Fortified milk and milk products
• Egg yolk
• Oily fish such as salmon, sardines and mackerel
• Fortified cereals and some packaged foods (check the label)
• Mushrooms that have been dried in sunlight

A vegetarian diet offers few reliable sources, so sunlight — and, if a test shows a shortfall, a prescribed supplement — usually do more of the work.

How sunlight helps

Skin makes vitamin D when direct sunlight reaches it, so arms, legs or the back need to be uncovered. Sitting behind glass does not work. How long you need depends on your skin tone, the season, where you live and the time of day.

When are supplements appropriate?

Only when a test shows a shortfall and a doctor prescribes one. Because the body stores vitamin D, taking large doses without needing them can cause harm. The high doses that circulate online are not meant for everyone — the amount, the form and how long to take it are clinical decisions.

Simple ways to prevent it

• Spend some time in gentle morning sun on several days of the week
• Keep milk, curd and eggs in your regular diet
• Get tested rather than waiting it out if tiredness persists
• Finish the course if a deficiency is found, and retest as advised