Factors that determine vitamin D levels - Sunlight
Factors that determine vitamin D levels
1. Sunlight
There are various factors that affect the amount of sunlight an individual will be exposed to, and therefore their vitamin D levels.
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Seasonality
In the UK, the body cannot synthesise any vitamin D from October to late March/ beginning of April, as the ultraviolet sunlight is not at the appropriate wavelength. The body relies on sun exposure gained during the summer months, which peak during the autumn months. Levels then reduce over the winter months and reach their lowest levels during spring.
Seasonal variations in vitamin D insufficiency (or worse) in the UK9
Autumn
Spring
Latitude
The position of the sun will affect the strength at which vitamin D synthesis will be stimulated. For the UK north of Cambridge, the sun stimulates vitamin D synthesis from sunlight for four months of the year, whereas south of this can stimulate this reaction for five months.10
Time of day
Between 11am and 3pm is the optimal time for individuals to synthesise vitamin D, when sunlight is strongest. Sufficient amounts can made by being in the sun for short periods of time (although people with darker skin may need longer).11
Amount of exposure
This will be affected by factors such as weather conditions, wearing clothing that completely covers the skin and widespread use of sun-blockers. Customers will not be able to synthesise vitamin D indoors sitting next to a window as ultraviolet B rays will not get through.3
Skin type and age
People with darker skin, such as those of African or South Asian origin, are not able to produce as much vitamin D, as darker pigments interfere with UV light reaching the appropriate layer of the skin.
As a person ages, their skin will become thinner, which reduces the efficiency of vitamin D synthesis.
