Why Is My Vitamin D Low? Causes in Women Explained

Why Is My Vitamin D Low? Causes of Vitamin D Deficiency in Women

If a blood test has shown that your vitamin D is low, your first question is probably not what vitamin D does.

It is:

Why is my vitamin D low in the first place?

Low vitamin D can happen for several reasons. You may not be making enough through sunlight, your diet may provide very little, your body may have difficulty absorbing or processing it, or certain medicines and health conditions may affect your vitamin D status.

For women in the UK, season and sunlight exposure are particularly important. Pregnancy, breastfeeding and later-life bone health can also make vitamin D intake more important at certain stages of life.

If you are trying to understand whether symptoms such as tiredness, muscle weakness or bone discomfort could be related, read our guide to vitamin D deficiency symptoms.

This article focuses on the other half of the question: why vitamin D becomes low and what you can do next.

What Does Vitamin D Actually Do?

Vitamin D is a fat-soluble vitamin with an important role in maintaining normal bones, muscles and immune function.

One of its best-established functions is helping the body absorb and use calcium.

Your body can obtain vitamin D in three main ways:

• Producing it in the skin after exposure to sunlight
• Getting a smaller amount through food
• Taking vitamin D through supplements

When these sources are not sufficient, vitamin D levels can fall.

Why Is My Vitamin D Low?

There is rarely one explanation that applies to everyone.

Low vitamin D usually comes down to one or more of the following:

1. Not making enough vitamin D from sunlight
2. Not consuming much vitamin D through food or supplements
3. Difficulty absorbing vitamin D
4. Difficulty processing or activating vitamin D
5. Medicines or medical conditions affecting vitamin D metabolism
6. Higher individual risk because of age, skin pigmentation or lifestyle

Understanding which of these applies to you is more useful than simply buying the highest-dose supplement you can find.

1. Not Getting Enough Sunlight

For most people, sunlight is an important natural source of vitamin D.

When ultraviolet B radiation reaches the skin, it triggers vitamin D production.

If you spend very little time outdoors, however, your opportunity to make vitamin D naturally becomes much smaller.

This can affect people who:

• Work indoors throughout the day
• Work from home and rarely go outside
• Are housebound
• Spend long periods in hospitals or care settings
• Regularly avoid outdoor daylight

Modern lifestyles can make this surprisingly common.

You can have a balanced diet, exercise regularly and still have relatively little direct daylight exposure.

2. Living in the UK During Autumn and Winter

Location matters.

In the UK, sunlight during roughly October to early March is generally not strong enough for most people to make sufficient vitamin D through their skin.

That means someone who had adequate sunlight exposure during summer can still become more dependent on food and supplements during winter.

UK guidance therefore recommends that adults and children over four consider taking 10 micrograms, or 400 IU, of vitamin D per day during autumn and winter.

Some higher-risk groups are advised to consider this throughout the year.

We explain the seasonal recommendation in much more detail in our UK guide to vitamin D in autumn and winter.

3. Spending Most of Your Time Indoors

You do not need to be completely housebound for indoor life to affect your vitamin D opportunity.

Think about a typical weekday:

• You wake up indoors
• Commute in a car, train or bus
• Work indoors for eight hours
• Travel home
• Spend the evening indoors

During winter, you may leave home before sunrise and finish work after dark.

This is one reason vitamin D risk is not limited to people who are visibly unhealthy or elderly.

4. Darker Skin

Skin pigmentation affects vitamin D production from sunlight.

Melanin helps protect the skin from ultraviolet radiation, but higher levels of melanin also mean more UV exposure is generally required to produce the same amount of vitamin D.

UK guidance specifically identifies people with darker skin, including people from African, African-Caribbean and South Asian backgrounds, as being at greater risk of not making enough vitamin D from sunlight.

For these groups, year-round vitamin D supplementation may be worth considering in line with UK guidance.

5. Covering Most of Your Skin Outdoors

Clothing can also affect how much skin is available for sunlight-induced vitamin D production.

People who regularly cover most of their skin outdoors for cultural, religious, medical or personal reasons may produce less vitamin D from sunlight.

This does not mean someone should change how they dress.

It simply means vitamin D from food or supplementation becomes more important.

6. Eating Very Few Foods Containing Vitamin D

Unlike nutrients such as vitamin C, vitamin D is naturally present in relatively few foods.

Sources include:

• Oily fish such as salmon, sardines, herring and mackerel
• Egg yolks
• Red meat
• Liver
• Foods fortified with vitamin D

Because the list is comparatively limited, it can be difficult to rely on food alone for your entire vitamin D intake, particularly during UK winter.

Can a Vegan Diet Cause Low Vitamin D?

A vegan diet does not automatically cause vitamin D deficiency.

However, several naturally occurring dietary sources of vitamin D are animal-derived.

Someone following a vegan diet may therefore need to pay closer attention to:

• Fortified plant-based foods
• Fortified cereals
• Vitamin D supplements
• The type of vitamin D used in a supplement

Vitamin D2, or ergocalciferol, is commonly suitable for vegan diets.

Some vitamin D3 supplements are also vegan, but D3 can alternatively be sourced from lanolin, so checking the label matters.

7. Pregnancy and Breastfeeding

Pregnancy does not automatically mean that you are vitamin D deficient.

However, maintaining adequate vitamin D is particularly important during pregnancy and breastfeeding.

UK guidance recommends vitamin D supplementation during pregnancy, with additional attention warranted for women who also have other risk factors such as:

• Darker skin
• Limited sunlight exposure
• Covering most of the skin
• Spending most of the day indoors

If you are pregnant, do not start high-dose vitamin D to treat a suspected deficiency yourself.

Follow pregnancy-specific advice from your midwife, GP, pharmacist or other healthcare professional.

8. Problems Absorbing Vitamin D

Vitamin D is fat-soluble.

That means conditions affecting digestion or fat absorption can sometimes make it harder for the body to absorb vitamin D normally.

Examples can include certain:

• Malabsorption disorders
• Inflammatory bowel conditions
• Coeliac disease
• Other gastrointestinal conditions affecting nutrient absorption

People with a diagnosed digestive condition should not assume that an ordinary over-the-counter supplement is automatically enough to correct a deficiency.

The underlying absorption issue may affect how deficiency needs to be managed.

9. Previous Weight-Loss Surgery

Certain types of bariatric or weight-loss surgery change how the digestive system handles food and nutrients.

This can increase the risk of deficiencies in several vitamins and minerals, including vitamin D.

People who have undergone bariatric surgery usually need specific long-term nutritional monitoring rather than relying on general supplement advice.

10. Kidney Problems

Your kidneys are involved in converting vitamin D into forms the body can use.

Advanced chronic kidney disease can therefore affect vitamin D metabolism as well as calcium and phosphate balance.

This is different from simply having a low dietary intake.

If kidney disease is involved, vitamin D treatment and monitoring should be managed with professional medical guidance.

11. Liver Disease

The liver is also involved in vitamin D metabolism.

Severe liver disease can therefore contribute to problems maintaining or processing vitamin D.

Again, this is not something that should be managed simply by increasing the number of vitamin gummies you take.

12. Certain Medicines

Some medicines can affect vitamin D metabolism or increase the risk of low vitamin D levels.

For example, long-term use of certain anti-epileptic medicines can affect bone metabolism and vitamin D status.

Other medicines can also alter vitamin D or calcium metabolism.

If you take long-term medication and have been told your vitamin D is low, ask your pharmacist or doctor whether your medication could be relevant.

Do not stop prescribed medicine because of something you read online.

13. Age

The skin's ability to produce vitamin D can become less efficient with age.

Older adults may also spend less time outdoors or have other health factors that increase their risk.

This is why older adults, particularly people who are housebound or living in care settings, receive additional attention in vitamin D guidance.

Does Menopause Cause Low Vitamin D?

Menopause itself should not automatically be described as a direct cause of vitamin D deficiency.

However, vitamin D becomes particularly relevant to bone health as women get older.

After menopause, declining oestrogen levels accelerate bone loss, increasing the importance of protecting bone health through appropriate nutrition, physical activity and medical care where needed.

Because vitamin D helps the body absorb calcium and supports normal bones, maintaining adequate vitamin D remains important during and after menopause.

That does not mean vitamin D supplements prevent or treat osteoporosis on their own.

Does Body Weight Affect Vitamin D Levels?

Research has repeatedly found an association between higher body weight and lower circulating vitamin D levels.

Because vitamin D is fat-soluble, its distribution in the body can differ with greater amounts of body fat.

However, this does not mean body weight alone proves someone is deficient.

Vitamin D status should be considered alongside other risk factors and clinical circumstances.

Can Stress Cause Vitamin D Deficiency?

Stress itself is not generally considered a primary direct cause of vitamin D deficiency.

But lifestyle changes associated with chronic stress could indirectly matter.

For example, someone who is stressed may:

• Spend more time indoors
• Eat a less varied diet
• Sleep poorly
• Have less consistent daily routines

If your vitamin D is genuinely low, it is better to investigate established causes than simply attributing it to stress.

Can Low Vitamin D Cause Symptoms?

Yes, severe vitamin D deficiency can cause health problems, but mild deficiency may produce few obvious symptoms.

This is one reason symptoms alone cannot confirm your vitamin D status.

Possible problems associated with significant deficiency can include bone or muscle symptoms and osteomalacia in adults.

Many non-specific complaints sometimes associated with low vitamin D, such as tiredness, can also have dozens of other causes.

If symptoms are your main concern, continue with our complete guide to vitamin D deficiency symptoms and signs.

How Do You Know If Your Vitamin D Is Actually Low?

Vitamin D status can be assessed using a blood test measuring 25-hydroxyvitamin D, or 25(OH)D.

In UK public-health guidance, a blood concentration below approximately 25 nmol/L is commonly used to define low vitamin D status or deficiency.

Clinical interpretation can be more nuanced, and laboratories or healthcare professionals may use additional ranges depending on your circumstances.

That is why a number from a blood test should be interpreted alongside your symptoms, medical history and risk factors rather than through an online chart alone.

Should Everyone Get a Vitamin D Blood Test?

No.

Routine vitamin D testing is not recommended for every healthy person.

UK guidance generally reserves testing for situations such as:

• Symptoms that could suggest deficiency
• Very high risk of deficiency
• Bone conditions where vitamin D status affects management
• Specific clinical reasons

If you simply have a recognised risk factor such as limited winter sunlight, prevention through an appropriate everyday supplement may be recommended without routine testing.

If you have symptoms, a medical condition, take relevant medication or believe you may be severely deficient, speak to a healthcare professional.

Can Vitamin D Deficiency Be Fixed With Food?

Food can contribute vitamin D, but correcting a diagnosed deficiency through diet alone may be difficult.

Vitamin D is naturally present in relatively few foods.

A balanced diet can still include useful sources such as oily fish, eggs and fortified foods, but treatment for a confirmed deficiency may involve supplementation at amounts determined by a healthcare professional.

Do not confuse a routine daily supplement designed to help prevent deficiency with the doses sometimes prescribed to correct a clinically diagnosed deficiency.

Should You Take Vitamin D Supplements?

For the general UK population, guidance recommends considering 10 micrograms, or 400 IU, per day during autumn and winter.

Some people should consider vitamin D throughout the year, particularly those who:

• Spend very little time outdoors
• Usually cover most of their skin outdoors
• Have darker skin

If you want to understand gummy formulations specifically, read our Vitamin D Gummies: Effectiveness, Dosage & Safety Guide.

Can You Take Vitamin D in a Multivitamin?

Yes.

Vitamin D does not necessarily need to come from a standalone vitamin D product.

A multivitamin may already provide the amount you intend to take.

For example, Yumi All Day Energy Multivitamin Gummies currently provide 10 micrograms of vitamin D per recommended two-gummy serving.

They use vitamin D2, or ergocalciferol, and combine it with vitamins A, C, E, B6, niacin, biotin and other nutrients.

That 10-microgram amount matches the standard UK general daily recommendation discussed above.

However, a normal daily multivitamin should not be presented as treatment for a diagnosed vitamin D deficiency.

If your doctor has confirmed a deficiency and recommended a different dose, follow that medical advice.

Check Your Other Supplements Before Adding Vitamin D

One easy mistake is taking several products that all contain the same nutrient.

You might take:

• A multivitamin
• A hair, skin and nails supplement
• A standalone vitamin D supplement

and unknowingly get vitamin D from all three.

Always check the amount per recommended daily serving.

Our UK guide to choosing gummy supplements explains serving size, NRV, overlapping ingredients and supplement labels in more detail.

Can You Take Too Much Vitamin D?

Yes.

Vitamin D is fat-soluble, so excessive supplementation over time can cause vitamin D toxicity and lead to too much calcium in the blood.

For most adults, NHS guidance says not to take more than 100 micrograms, or 4,000 IU, of vitamin D per day unless a healthcare professional has advised otherwise.

Taking more does not mean your vitamin D will improve in a safer or more useful way.

What Should You Do If Your Vitamin D Is Low?

If a blood test has confirmed low vitamin D, the best next step depends on how low the level is and why it may have happened.

Your plan may involve:

1. Identifying likely risk factors
2. Reviewing your diet
3. Reviewing sunlight exposure
4. Checking medicines or medical conditions
5. Using an appropriate vitamin D supplement
6. Following any treatment prescribed for confirmed deficiency
7. Repeating testing when medically appropriate

The important point is that prevention and treatment are not always the same thing.

A routine 10-microgram supplement may be suitable for everyday prevention in many adults, while someone with clinically significant deficiency may be advised to use a different regimen.

How Can You Reduce Your Risk of Low Vitamin D?

For many people, prevention is simpler than correcting a significant deficiency later.

A practical approach includes:

• Following UK seasonal vitamin D guidance
• Including vitamin D-containing or fortified foods in your diet
• Spending some time outdoors while following sun-safety advice
• Considering year-round supplementation if you are in a higher-risk group
• Checking the vitamin D already present in your supplements
• Seeking medical advice if you have symptoms or significant risk factors

For the UK seasonal approach specifically, read Do You Need Vitamin D in Autumn and Winter?.

Frequently Asked Questions

Why is my vitamin D low even though I go outside?

Outdoor activity is only one factor. Season, UK latitude, skin pigmentation, how much skin is exposed, diet, age, digestive conditions, medication and other health factors can all affect vitamin D status.

What is the most common cause of low vitamin D?

Insufficient sunlight exposure is one of the major causes and risk factors, particularly in countries such as the UK during autumn and winter. Diet, skin pigmentation and individual health circumstances can also contribute.

Why is vitamin D deficiency common in women?

The main causes of vitamin D deficiency are not exclusive to women. However, pregnancy, breastfeeding and later-life bone health make maintaining adequate vitamin D particularly relevant during certain stages of a woman's life. Lifestyle, skin pigmentation and sunlight exposure remain major factors.

Can pregnancy cause low vitamin D?

Pregnancy does not automatically cause deficiency, but pregnant women are an important group for maintaining adequate vitamin D intake. Women with additional risk factors such as darker skin or limited sunlight may require particular attention.

Does menopause cause vitamin D deficiency?

Menopause is not generally considered a direct cause of vitamin D deficiency. However, bone loss accelerates after menopause, so maintaining adequate vitamin D and calcium becomes especially relevant to overall bone health.

Can a vegan diet cause vitamin D deficiency?

Not automatically. However, several natural food sources of vitamin D are animal-derived, so people following a vegan diet may need to pay more attention to fortified foods and suitable vitamin D supplements.

Can stress make vitamin D low?

Stress itself is not considered a major direct cause of vitamin D deficiency. Lifestyle changes associated with chronic stress, such as spending more time indoors or eating a less varied diet, could indirectly affect vitamin D intake and exposure.

Can low vitamin D make you tired?

Low vitamin D can be associated with symptoms, but tiredness is very non-specific and can have many other causes. If persistent tiredness is affecting your daily life, it is worth discussing with a healthcare professional rather than assuming vitamin D is responsible.

How do I know if my vitamin D is low?

Vitamin D status can be measured using a 25-hydroxyvitamin D blood test. Symptoms alone cannot reliably diagnose deficiency.

What vitamin D level is considered deficient in the UK?

UK public-health guidance commonly defines low vitamin D status as a 25-hydroxyvitamin D concentration below 25 nmol/L. Clinical interpretation can vary depending on circumstances and laboratory guidance.

Should I take 10 micrograms of vitamin D every day?

UK guidance advises most adults to consider 10 micrograms daily during autumn and winter. People with limited sunlight exposure or darker skin may be advised to consider supplementation throughout the year.

Can vitamin D gummies help prevent deficiency?

Vitamin D gummies can provide vitamin D when they contain an appropriate amount and are taken according to the label. The gummy format itself is not what prevents deficiency. The vitamin D amount and consistent intake are what matter.

Are 10 micrograms and 400 IU the same?

Yes. For vitamin D, 10 micrograms is equivalent to 400 IU.

Can I take too much vitamin D?

Yes. Excessive vitamin D supplementation over time can be harmful. NHS guidance advises most adults not to exceed 100 micrograms, or 4,000 IU, per day unless instructed by a healthcare professional.

The Bottom Line

If your vitamin D is low, there may be more than one reason.

Common causes and risk factors include:

• Limited sunlight
• UK autumn and winter
• Spending most of your day indoors
• Darker skin
• Covering most of the skin outdoors
• Low dietary intake
• Pregnancy and breastfeeding
• Malabsorption
• Weight-loss surgery
• Certain medicines
• Kidney or liver conditions
• Older age

If you are concerned because you are experiencing symptoms, the next useful read is our complete guide to vitamin D deficiency symptoms.

If you are deciding how to supplement, see our Vitamin D Gummies: Effectiveness, Dosage & Safety Guide.

And for UK seasonal guidance, read Do You Need Vitamin D in Autumn and Winter?.

If you prefer vitamin D as part of a broader daily multivitamin, Yumi All Day Energy currently provides 10 micrograms of vitamin D per recommended two-gummy serving.

Important: This article is for general educational purposes and is not medical advice. Food supplements should not replace a varied, balanced diet or appropriate medical treatment. If you have a diagnosed vitamin D deficiency, significant symptoms, a malabsorption condition, kidney or liver disease, are pregnant or breastfeeding, or take medication that may affect vitamin D, speak to a qualified healthcare professional about the appropriate approach for you.