Vitamin D Deficiency: Symptoms, Best Foods and How Much You Need
Quick answer: Vitamin D helps your body absorb calcium and keeps bones and muscles working. The general recommended intake for most adults is 600 IU (15 mcg) a day, rising to 800 IU (20 mcg) after age 70. The usual upper limit is 4,000 IU (100 mcg) a day unless your doctor advises otherwise. Deficiency is confirmed only by a blood test.
Many people I see in clinic are surprised to learn they’re low in vitamin D, even in sunny countries. Indoor work, sunscreen, clothing, pollution and darker skin tones all reduce how much vitamin D the skin makes.
What does vitamin D do?
Vitamin D supports calcium absorption, bone strength, muscle function and normal immune activity. The NIH Office of Dietary Supplements notes that vitamin D is naturally present in very few foods, which is why deficiency is so common.
Common symptoms of vitamin D deficiency
Symptoms can be subtle or absent. Possible signs include:
- Tiredness and low energy
- Bone pain or lower back pain
- Muscle weakness or cramps
- Frequent illness
- Low mood
- Slow wound healing
In severe, long-term cases, deficiency can cause rickets in children and osteomalacia in adults. These symptoms overlap with many other conditions, so a blood test (25-hydroxyvitamin D) is the only reliable way to know.
Who is most at risk?
- People who spend most of the day indoors
- People with darker skin
- Adults over 65
- People who cover most of their skin outdoors
- Those with obesity
- People with fat-absorption conditions such as coeliac or inflammatory bowel disease
- Exclusively breastfed infants (ask your paediatrician about supplements)
How much vitamin D do you need?
| Age group | Recommended daily intake | Upper limit |
|---|---|---|
| Children and adults 1 to 70 years | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| Adults over 70 | 800 IU (20 mcg) | 4,000 IU (100 mcg) |
Doctors sometimes prescribe higher short-term doses to treat a confirmed deficiency. Don’t do this on your own.
Best food sources of vitamin D
- Oily fish such as salmon, sardines and mackerel
- Egg yolks
- Fortified milk, curd and cereals (check the label)
- Mushrooms exposed to UV light
- Fortified plant milks
Most people can’t meet their needs through food alone, so sensible sun exposure and, where needed, supplements play a role.
What about sunlight?
Short periods of midday sun on bare skin help the body make vitamin D. How much you need depends on your skin tone, location, season and time of day. Never risk sunburn to boost vitamin D.
Vitamin D2 vs D3
Both forms raise vitamin D levels, but D3 (cholecalciferol) is the form most commonly used in supplements. Take your supplement with a meal that contains some fat for better absorption.
Can you take too much vitamin D?
Yes. Excess vitamin D can raise blood calcium, causing nausea, weakness, kidney problems and heart rhythm issues. Stay within the 4,000 IU limit unless a doctor advises otherwise, and avoid doubling up with multiple supplements that each contain vitamin D.
How to fix low vitamin D: a practical plan
- Get tested to confirm your level.
- Add food sources like fish, eggs and fortified foods.
- Spend sensible time outdoors, without burning.
- Use a D3 supplement if your doctor recommends one.
- Retest after about 3 months to check your progress.
Frequently asked questions
What is the best time to take vitamin D?
Whenever you’ll remember, with your largest meal. Consistency matters more than timing.
How long does it take to correct vitamin D deficiency?
It often takes a few months, depending on your starting level and the dose your doctor prescribes.
Is 1000 IU of vitamin D safe daily?
For most adults, yes, as it’s well under the 4,000 IU upper limit. Check with your doctor first if you have kidney, heart or parathyroid conditions.
Can vitamin D deficiency cause hair fall or fatigue?
It may contribute to fatigue. Hair fall has many causes, so get a proper check-up.
Does vitamin D help with weight loss?
There’s no strong evidence that vitamin D alone causes weight loss.
The bottom line
Vitamin D deficiency is common but fixable. Test first, improve food and sun habits, and supplement at a safe dose if needed. For authoritative intake guidance, see the NIH Office of Dietary Supplements’ Vitamin D fact sheet for consumers. To fill gaps in your routine, you can also explore our supplement guides.
This article is for general information only and isn’t medical advice. Speak to a doctor or registered dietitian before starting any supplement, especially if you’re pregnant, on medication or have a medical condition.
