Vitamin D
In brief
Section titled “In brief”- Vitamin D is essential for immunity, hormones, energy, muscles, and metabolic balance
- 50% of Dutch adults have a deficiency in winter
- Sunlight provides 80% of the requirement, food only 20%
- Deficiency can be a marker for insulin resistance and lack of sunlight
- Supplementation: 3000 IU per day in autumn and winter, with overweight often more
What is vitamin D?
Section titled “What is vitamin D?”Vitamin D is in fact a hormone with a multitude of functions. The body produces vitamin D in the skin under the influence of UVB radiation from sunlight. This route provides as much as 80% of the requirement.
Vitamin D has two important functions:
| Function | Explanation |
|---|---|
| Endocrine | Facilitates calcium and phosphate absorption in the intestine and formation of healthy bone |
| Autocrine | Controls about 1000 genes (5% of the genome) in virtually all tissues |
The autocrine function inhibits proliferation and autoimmune reactions, and stimulates differentiation, insulin, and antibacterial activity.
Why deficiency is so common
Section titled “Why deficiency is so common”In the Netherlands, 50% of the adult population has a moderate or severe vitamin D deficiency in winter (without supplementation).
Risk factors
Section titled “Risk factors”| Factor | Effect |
|---|---|
| Little sunlight | October to March insufficient UVB radiation |
| Indoor work | Too little outdoor air |
| Overweight | Vitamin D is stored in fatty tissue and therefore remains low |
| Dark skin | Less cholecalciferol production |
| Covering clothing | Blocks UVB radiation |
| Higher age | Skin produces less vitamin D |
| Chronic kidney damage | Reduced activation |
Clinical characteristics of deficiency
Section titled “Clinical characteristics of deficiency”Recognize the signs of vitamin D deficiency:
- Fatigue and low energy
- Muscle pain, less strength, stiffer movement
- Susceptibility to infections, slow recovery
- Depression, irritability, sleep problems
- Higher inflammatory activity
- Lower insulin sensitivity
Blood values and measurement
Section titled “Blood values and measurement”Vitamin D status is measured via the 25(OH)D level (calcidiol) in the blood.
| Level | Assessment |
|---|---|
| 75-125 nmol/L | Optimal |
| 50-75 nmol/L | Mild deficiency |
| 25-50 nmol/L | Moderate deficiency |
| below 25 nmol/L | Severe deficiency |
Levels vary throughout the year:
- Highest values: September
- Lowest values: March
Consequences of prolonged deficiency
Section titled “Consequences of prolonged deficiency”A chronically poor vitamin D status leads to:
Direct consequences
Section titled “Direct consequences”- Secondary hyperparathyroidism
- Osteomalacia and osteoporosis
- Fall tendency and fractures
Associated conditions
Section titled “Associated conditions”- Cardiovascular disease
- Diabetes mellitus
- Autoimmune diseases
- Infections
- Cancer
Vitamin D deficiency can directly contribute to endothelial dysfunction, atherosclerosis, and hypertension via inflammation, proliferation, and RAAS activation.
Sunlight: the most important source
Section titled “Sunlight: the most important source”How sunlight works
Section titled “How sunlight works”In the skin, under the influence of UVB radiation (280-320 nm), 7-dehydrocholesterol is converted to cholecalciferol (vitamin D3).
| Aspect | Advice |
|---|---|
| Time | Between 10:00 AM and 3:00 PM |
| Duration | 15-30 minutes |
| Exposure | Face and forearms uncovered |
| Season | Only effective from April to September in the Netherlands |
Sunlight and life expectancy
Section titled “Sunlight and life expectancy”Swedish research shows that women with regular sunlight exposure live 1-2 years longer than women who avoid sunlight. Sunlight deprivation is sometimes called “the new smoking.”
Responsible sun exposure
Section titled “Responsible sun exposure”- Short, frequent exposure is better than long sessions
- Avoid burning through gradual build-up
- Vitamin D is also produced in the shade via reflection
- Sunscreen with SPF above 15 blocks cholecalciferol production
Food sources
Section titled “Food sources”Food contains insufficient vitamin D to meet daily needs, but does contribute:
| Source | Note |
|---|---|
| Fatty fish | Salmon, herring, mackerel, sardines — best food source |
| Egg yolks | Especially from free-range eggs |
| Butter | Preferably from grass-fed cows |
| Pork | Small amounts |
| Fortified products | Margarine, dairy |
Supplementation
Section titled “Supplementation”When to supplement?
Section titled “When to supplement?”In autumn and winter (October-March), supplementation is necessary for most people due to insufficient sunlight.
Dosage
Section titled “Dosage”| Situation | Dosage |
|---|---|
| Maintenance | 3000 IU (75 mcg) per day |
| With overweight | Often 2x as much needed |
| Severe deficiency | Loading schedule: 25,000 IU per week for 3 months |
Practical tips
Section titled “Practical tips”| Tip | Why |
|---|---|
| Take with meal with fat | Improves absorption |
| Magnesium with it | 200-300 mg bisglycinate as cofactor |
| Vitamin K2 (MK-7) | Supports bone and blood vessels |
| Check after 4-6 months | Check if target value is reached |
Lifestyle and metabolism
Section titled “Lifestyle and metabolism”Vitamin D levels are strongly influenced by lifestyle:
| Lifestyle factor | Effect |
|---|---|
| Weight loss | Raises levels as stored vitamin D is released |
| Insulin sensitivity | Supports activation of vitamin D in liver and kidneys |
| Exercise | Improves metabolism and insulin sensitivity |
| Protein-rich nutrition | Supports muscles and metabolism |
| Healthy fats | Olive oil, butter — improve absorption |
Practical daily steps
Section titled “Practical daily steps”- Daily outdoor light — preferably midday
- Fatty fish twice a week — salmon, herring, mackerel
- Protein-rich and unprocessed eating — with healthy fats
- Strength training and walking — improves insulin sensitivity
- Supplementation in autumn/winter — 3000 IU per day with a meal
Summary
Section titled “Summary”Veelgestelde vragen
Why is vitamin D deficiency so common?
In the Netherlands, 50% of adults have a moderate or severe deficiency in winter. Causes are: little sunlight (October-March), indoor work, overweight (vitamin D is stored in fat), dark skin, covering clothing, and stress.
What is a good vitamin D level?
The optimal value is 75-125 nmol/L. Below 50 nmol/L there is deficiency, below 25 nmol/L severe deficiency. The 25(OH)D level is measured via blood test.
How much vitamin D should I supplement?
In autumn and winter, 3000 IU (75 mcg) per day is sufficient for most people. With overweight, often twice as much is needed. Take supplements with a meal containing fat for better absorption.
Can I get enough vitamin D from food?
No, food provides only 20% of the requirement. The main source is sunlight (80%). Fatty fish, eggs, and butter contain vitamin D, but not enough to meet daily needs.
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Medical Disclaimer: The information provided by Stichting Je Leefstijl Als Medicijn regarding lifestyle, diseases, and disorders should not be construed as medical advice. Under no circumstances do we advise people to alter their existing treatment. We recommend that people with chronic conditions seek advice regarding their treatment from qualified medical professionals.