Vitamin D is well known for its role in building and preserving bone, but in recent years there has been increasing interest in other functions linked to vitamin D.
It is becoming clear that many aspects of good health are related to your vitamin D levels.
How is Vitamin D Produced?
Vitamin D is fat soluble and is made from cholesterol when skin is exposed to UVB rays in sunlight.
It is thought that around 15-20 minutes exposure to direct sunlight each day is required to maintain healthy levels.
The metabolism of vitamin D is complex, and several forms exist.
Vitamin D2 (ergocalciferol) found in plants and vitamin D3 (cholecalciferol) from animals are precursors to active forms of vitamin D.
Once synthesised in the skin, conversion to active vitamin D occurs in the liver and the kidneys.
Does Food Contain Vitamin D?
Some foods contain vitamin D, but it is debated as to how much these contribute to overall levels.
The most significant levels of vitamin D are found in animal foods including oily fish (5-16 μg/200-640 IU per100 g) and egg yolks (12.6 µg/504 IU per 100 g) (1).
Meat and offal also contain vitamin D (0.11.5 μg/4-60 IU per 100 g) (2).
Wild mushrooms and cultivated mushrooms exposed to UVB light contain vitamin D2.
Functions
Once thought to be limited to bone health, vitamin D is now recognised as being involved in a variety of aspects of health and is considered to be a hormone rather than a vitamin.
Vitamin D receptors are found in numerous parts of the body including the heart, stomach, skin, brain, breast and prostate (3).
Active vitamin D binds to the vitamin D receptor (VDR) which can regulate the expression of a variety of genes – this is why recent research is showing vitamin D to have a role in many functions.
These include:
- Increasing intestinal absorption of bone supportive nutrients – calcium and phosphate
- Promoting healthy bone remodelling
- Immune support – enhancing natural defences against foreign substances and pathogens (4)
- Regulating actions involved in cancer development – cell proliferation and differentiation
- Involvement in modulating the inflammatory response (5)
- Playing a role in insulin secretion and blood sugar balance (6)
- Involvement in systems that regulate blood pressure (7)
How Much Vitamin D is Needed?
Current government recommendations for daily intake of vitamin D are general recommendations that do not take into account personal circumstances, lifestyle and the presence of chronic conditions.
Recommendations also vary according to country and the EU, USA and Canada may have different recommendations.
In the UK, it is suggested that infants up to the age of 1 year old should have between 340iu (8.5µg) and 400iu (10µg) of vitamin D a day.
Children, adults and pregnant and breastfeeding women should have around 400iu (10µg) of vitamin D a day (8).
The tolerable upper intake, the level which is deemed to be safe to take on a daily basis, has been set at much higher levels than the recommended daily intake.
These are as follows:
Infants up to the age of 1 year old – 1000iu (25µg)
Children aged 1-10 years – 2000iu (50µg)
Children aged 11 and older, adults and pregnant women – 4000iu (100µg) (9)
Testing Vitamin D Levels
There has been a rise in testing for vitamin D levels and it is now routinely run through the NHS .
Private laboratories offer simple at home pin prick blood tests.
Vitamin D levels are usually reported in nmol/L or ng/L depending on the country.
The interpretation of the results and recommended levels also varies according to different organisations.
In the UK it is recommended that vitamin D levels should not fall below 25 nmol/L (10ng/ml) at any time of the year (10) and could be classed as ‘deficient’.
At this present time there is no firm recommendation of what an optimal level of vitamin D is.
Some sources suggest that sufficient levels are 50nmol/L (30ng/ml) and that an optimal level may be around 70–80nmol/L (28-32ng/ml) (11,12).
The Vitamin D Council suggest the following (13):
| Deficient | 0-30ng/ml (0-75mnol/L) |
| Insufficient | 31-39 ng/ml (77.5-97.5nmol/L) |
| Sufficient | 40-80 ng/ml (100-200nmol/L) |
Deficiency Signs
Vitamin D deficiency is now thought to be common.
This can be down to a number of reasons including lack of sunlight exposure, the use of strong sun creams or sun blocks, climate, dark coloured skin, nocturnal habits like shift work, sedentary lifestyle with large periods of time spent indoors, age, body mass and genetic factors.
Some experts think vitamin D levels decrease in response to acute inflammation and infection, suggesting that low vitamin D levels may actually reflect an underlying issue (14,15).
Signs and symptoms associated with vitamin D deficiency include:
- Soft weak bones, abnormal skeletal growth
- Bone pain
- Muscle weakness
- Fatigue
- Depression
- Frequent, infections, colds and flu
Getting Enough Vitamin D
As vitamin D influences so many functions in the body it follows there are wide reaching effects of vitamin D deficiency.
Low vitamin D levels have been linked to osteoporosis (16), poor blood sugar balance, Type 2 diabetes (17), autoimmune conditions like multiple sclerosis, rheumatoid arthritis and autoimmune thyroid disease (18), and even cognitive issues like Alzheimer’s (19) and dementia (20).
Vitamin D is fat soluble and may be stored – it is thought to remain in the body for up to 3 weeks.
But it is still advisable to maintain a good vitamin D intake.
As the primary source is from sunlight exposure, getting 15-20 minutes of sun on the skin daily is optimal.
If you have dark skin exposure may need to be longer. Avoid exposing the skin during 11am and 3pm as this is when the suns rays are strongest. If prolonged exposure to the sun throughout the day is likely to occur use a natural sun cream after the first 20 minutes.
Eating breakfast outdoors or going for an early morning walk are good ways to get your sun exposure.
Including oily fish and eggs in your diet is important.
Aim for 2-3 portions of oily fish such as salmon, herring, mackerel, sardines, trout or tuna a week.
Eating up to 3 eggs a day does not seem to negatively affect cholesterol levels (21), as was once thought, and so regular egg intake will help to contribute to vitamin D levels.
As the evidence is showing that vitamin D may be reduced in times of inflammation or infection, adopting an anti-inflammatory diet may help to prevent vitamin D levels from reducing.
A good anti-inflammatory diet includes eating 8-10 portions of fruit and vegetables a day and including a wide variety of colours – the more colourful the better.
This is because they fruit and vegetables contain different plant polyphenols that can have potent antioxidant and anti-inflammatory actions.
Ensuring you hit your optimal fruit and vegetable intake can be tracked with the use of a rainbow food chart – simply tick off or add in the portions you have eaten that day.
This also helps you to track which colours or fruits and vegetables you may need to focus on – it can be very easy to fall into the habit of choosing the same foods, day in day out.
Keep red meat and dairy low in the diet and opt for organic grass fed meat or poultry as these generally have a higher omega 3 content, pre-cursors to anti-inflammatory molecules.
Taking a vitamin D supplement may be wise particularly in the autumn and winter or if you have dark skin, are vegan or spend large periods of time indoors.
Ensure that the supplement contains vitamin D3 as this is the better form.
If you would like to know more about your vitamin D levels and health and are interested in testing, then a consultation with an experienced Personalised Health practitioner could be beneficial.
We’re dedicated to providing you with both insightful information and evidence-based content, all orientated towards the Personalised Health approach.
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