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Vitamin D is often called the "sunshine vitamin", yet low vitamin D is surprisingly common. Researchers estimate that around one billion people worldwide have deficient levels, and many more have levels considered insufficient. Our earlier article, "6 Good Sources of Vitamin D", introduced the topic. This updated guide explains why so many people fall short and practical ways to support healthy levels.

What Does Vitamin D Do?

Vitamin D is unusual: it acts more like a hormone than a typical vitamin. Its key roles include:

• Bone health: helping the gut absorb calcium and phosphorus for strong bones and teeth.
• Muscle function: supporting muscle strength; low levels are linked to weakness and falls in older adults.
• Immune function: vitamin D receptors are found on many immune cells.
• Cell regulation: vitamin D receptors exist in tissues throughout the body.

Severe deficiency causes rickets in children and osteomalacia (soft bones) in adults.

How Your Body Makes Vitamin D

When ultraviolet B (UVB) light hits your skin, it converts a form of cholesterol into vitamin D3. The liver and kidneys then convert it into its active form. This sounds simple, but many factors reduce how much you make:

• Latitude: above roughly 37 degrees north (around San Francisco's latitude), UVB is too weak in winter for meaningful vitamin D production.
• Season and time of day: UVB is strongest around midday in summer.
• Skin tone: more melanin means more sun exposure is needed to produce the same amount.
• Age: older skin produces vitamin D less efficiently.
• Sunscreen and clothing: both reduce UVB reaching the skin.
• Indoor lifestyles: office work, commuting and screen time keep many of us indoors.
• Glass: windows block most UVB, so sitting by a sunny window does not help.

Who Is Most at Risk?

• People living in northern latitudes, especially in winter
• People with darker skin
• Older adults
• People who are housebound or work indoors
• People with obesity, as vitamin D is stored in fat tissue
• Those with conditions affecting fat absorption, such as Crohn's or coeliac disease
• Breastfed infants, who are often recommended a supplement by paediatricians

Signs of Low Vitamin D

Many people have no obvious symptoms. When they occur, they can include fatigue, bone or back pain, muscle aches and weakness, low mood and frequent infections. These symptoms are common to many conditions, so testing is the only reliable way to know.

Testing Your Level

A simple blood test measures 25-hydroxyvitamin D. The US Institute of Medicine considers 20 ng/mL (50 nmol/L) adequate for bone health in most people, while some organisations suggest higher targets. Ask your doctor to interpret your result and recommend an appropriate amount if you are low.

Natural Sources of Vitamin D

1. Sensible sun exposure

Short periods of midday sun on arms and legs, without burning, help many people make vitamin D in spring and summer. Balance this with skin cancer prevention: never let your skin burn.

2. Fish liver oils

Cod liver oil is one of the richest natural food sources. Traditional options include Green Pasture Fermented Cod Liver Oil and Fermented Skate Liver Oil, which contain naturally occurring vitamin D, with levels that vary by batch.

3. Oily fish

Salmon (especially wild), sardines, mackerel, herring and trout are good sources.

4. Egg yolks

Eggs from hens with outdoor access tend to contain more vitamin D.

5. UV-exposed mushrooms

Mushrooms exposed to sunlight or UV lamps produce vitamin D2.

6. Fortified foods

Many milks, plant milks, cereals and orange juices are fortified with vitamin D.

Vitamin D Works With Other Nutrients

• Calcium: vitamin D helps absorb it.
• Magnesium: needed to activate vitamin D; many diets are low in it. See our article on trace minerals.
• Vitamin K2: helps direct calcium to bones; read our butter oil and vitamin K2 guide.
• Dietary fat: vitamin D is fat-soluble, so take it with a meal containing fat.

Can You Get Too Much?

Yes. The body cannot overdose on vitamin D from sunlight, but excessive supplement intake over time can cause high blood calcium, with symptoms such as nausea, weakness and kidney problems. The US tolerable upper intake level for most adults is 4,000 IU per day unless a doctor advises otherwise. If you combine several products, such as cod liver oil plus a multivitamin, add up the totals.

Vitamin D2 vs. D3

Vitamin D comes in two main forms. D3 (cholecalciferol) is made in human skin and found in animal foods such as fish liver oils, oily fish and egg yolks. D2 (ergocalciferol) comes from fungi such as UV-exposed mushrooms and is used in some fortified foods. Several studies suggest D3 is more effective at raising and maintaining blood levels, which is why many supplements use it. Vegans can find D3 made from lichen.

A Simple Vitamin D Plan

1. Get your level tested.
2. Spend safe time outdoors when the sun is strong enough.
3. Eat oily fish twice a week and include eggs.
4. Consider a traditional fish liver oil in darker months, with professional guidance.
5. Retest after a few months if you are correcting a deficiency.

The Takeaway

Vitamin D deficiency is common because modern life keeps us indoors and many places lack strong year-round sunshine. Combining safe sunlight, nutrient-dense foods and, where appropriate, traditional fish liver oils is a practical way to support healthy levels.

Related Articles

• Vitamin A Explained: Retinol vs. Beta-Carotene and Why Balance Matters
• Magnesium: Signs You May Be Low and the Best Food Sources
• Omega-3 vs. Omega-6: Understanding Your Fat Balance

Disclaimer: This article is for general educational purposes only. These statements have not been evaluated by the Food and Drug Administration. Live Pine products are not intended to diagnose, treat, cure or prevent any disease. Always consult a qualified healthcare professional before starting a new supplement, especially if you are pregnant, nursing, taking medication or managing a health condition.