Vitamin D

Vitamin D helps your body to absorb calcium to maintain strong and healthy bones, to fight infections, and to maintain a healthy weight. Your body makes most of the vitamin D you need from sunshine and also absorbs a small amount from food. Low vitamin D can lead to low energy, more stress fractures, increased inflammation, and weaker muscles.

What is Vitamin D?

Vitamin D is an essential fat-soluble vitamin. Your body makes most of the vitamin D you need from sunlight and can absorb a small amount from food.

What do you need Vitamin D for?

Vitamin D helps your body to:

• Absorb calcium – to maintain strong and healthy bones, teeth and muscles.

• To fight infections – maintaining a strong immune system.

• To maintain a healthy weight.

Low levels of vitamin D have been linked to low energy, more stress fractures, increased inflammation and weaker muscles.  

How do I measure my Vitamin D levels?

You can check your vitamin D levels with an at-home finger prick blood test kit such as and you may wish to consult your doctor / medical professional about your results.

This test will measure your levels of 25-hydroxy vitamin D against the reference ranges of:

• Deficient – Under <30 nmol/L.

• Insufficient – Between 30-50 nmol/L.

• Normal range – Over >50 nmol/L.

• Excess – Over >200 nmol/L.

Although what is an 'ideal' vitamin D level remains contentious, around 75nmol/L is considered optimal for health.  

If you are not within an optimal range of vitamin D levels in your body, it is important to understand what could be causing this and what you can do to adjust your levels for better health.

What can influence my Vitamin D levels? 

• Skin exposure to the sun - the greater amount of skin exposure = greater available area for vitamin D synthesis.

• Latitude / distance from the equator -  the higher the latitude, the less UVB exposure for vitamin D production.

• Time of year & season - there tends to be limited / no vitamin D synthesis in winter at higher latitudes, for example in the UK, from October to the end of March, there is no UV radiation in the appropriate wavelength for making vitamin D.  A UVB wavelength in the range of 290-320nm is required for vitamin D synthesis to take place.

• Age - the ability to synthesise vitamin D decreased with age.

• Skin colour - melanin absorbs UVB, so the greater the skin pigmentation, the longer it takes to make vitamin D.

• Sunscreen use - using sunblock as low as SPF-15 can reduce vitamin D production by 98%.

• Body fat - vitamin D is taken up by fat cells, leaving less in circulation.

• Glass - this allows sun exposure i.e. whilst driving, but glass absorbs UBV, therefore vitamin D synthesis is not stimulated.

What can I do to impact my Vitamin D levels?

There are 3 main ways you can impact your vitamin D levels for optimal health: 

• Food sources –Vitamin D is found in oily fish, liver, eggs and some fortified foods.  Although dietary sources of vitamin D can help increase your levels slightly, it is hard to get enough vitamin D from food alone.

• 'Safe' sun exposure – Extra sun exposure can help boost your vitamin D levels when there is a UVB wavelength in the range of 290-320nm.  So, for the UK, this advice would only apply from the start of April to the end of September.  If you are out for long periods of time, at a greater risk of skin damage, it is recommended to cover up and wear sun protection.

• Vitamin D supplements.

Unless you are in a specialist at-risk health group, for example are pregnant, breastfeeding, or have complex underlying health concerns e.g. chronic kidney disease, there are some specific ways you can optimise your vitamin D levels, according to your level of of 25-hydroxy vitamin D:

• Deficient – Under <30 nmol/L.  We recommend consulting your doctor immediately for appropriate treatment to correct this. 

• Insufficient – Between 30-50 nmol/L. We recommend taking a vitamin D supplement that provides 2,000 IU per day and re-test your vitamin D periodically every 3 months and adjust your vitamin D dose according to the results.  

• Sub/normal range – Between 50 - 75 nmol/L. We recommend taking a vitamin D supplement that provides 1,000 IU per day and re-test your vitamin D periodically every 3 months and adjust your vitamin D dose according to the results. 

• Optimal – On or over >75 nmol/L.  Your current diet, lifestyle and sun exposure is optimising vitamin D levels. To maintain an optimal vitamin D level: 

1. Either - safe sun exposure. The amount of time you need in the sun to make enough vitamin D is different for everyone. For most people this will be a few minutes of sun exposure in the middle of the day (mostly between 11am and 3pm) with forearms or lower legs uncovered without sunscreen (applicable when UVB wavelength of 290-320nm occurs - in the UK this would be between April - September). But more is not better. Never let your skin redden or burn in the sun.

2. Or - taking a vitamin D supplement that provides 1,000 IU per day and re-test your vitamin D periodically every 3 months to ensure you stay in the optimal range. 

• Excess – Over >200 nmol/L. Your vitamin D levels are too high. We recommend you reduce or stop taking a vitamin D supplement and re-test your vitamin D periodically every 3 months to help you achieve optimal vitamin D status. 

Recommended Vitamin D supplement for flexible dosing