The big question

How much sun do I need to get my vitamin D quota?

Fascinating article by Cancer Research raises the topic – how much vitamin D to we need and how much time do we need to spend outside to get it?

The sun’s UV rays are the main cause of skin cancer, but we also need some sunshine to generate vitamin D for musculoskeletal health. Vitamin D helps regulate the amount of calcium and phosphate in the body. These nutrients are needed to keep bones, teeth and muscles healthy. A lack of vitamin D can lead to bone deformities such as rickets in children, and bone pain caused by a condition called osteomalacia (softening of the bones) in adults.

The amount of sun you need to generate enough vitamin D varies depending on your skin. But it has been unclear how long people might need to spend in the sun to generate enough vitamin D while minimising their skin cancer risk.

A Cancer Research-funded study looked at 39 people of different skin types who were exposed to low levels of UV (ultra-violet), with UV doses related participants’ burning risk. As the dose of UV increased towards their individual burning level, there was an increase in both vitamin D levels and DNA damage seen in skin samples. For all skin types. these factors seem to be completely intertwined.

They found that the darker the skin colour, the closer the DNA damage was to the surface. This suggests there’s DNA damage happening before skin burns and that it may be more likely to lead to problems in lighter skin types than darker ones.

People with darker skin can be encouraged to use sub-sunburn UV-exposure to enhance their vitamin D. In people with lighter skin, basal cell damage occurs at the same time as vitamin D synthesis at very low UV levels, explaining their high skin cancer incidence.

In essence, they believe that people with darker skin can be encouraged to expose their skin somewhat to the sun, without burning, to get vitamin D with very low risk of skin cancer. However, for people with lighter skin who are easy burners, even very low doses of UV can damage the cells in lower layers of the skin.

How long do we need to spend in the sun to make enough?

The study estimates that nine minutes of lunchtime sunlight each day would be enough for Caucasians to stay above the "deficient" category of vitamin D level throughout the year. This figure assumes that people would be in shorts and t-shirts for June to August, while only having their hands and faces exposed from March to June and for September. Our bodies start to break down vitamin D when we’re generating a lot of it so you can’t do a week all in one go. Little and often does seem to be the key.

With the same conditions, even people with darker brown skin that hardly ever burns and easily tans – such as people of South Asian origin –and may only need 25 minutes.

In the UK between October and early March we normally don't get enough vitamin D from sunlight.

Where else can I get my vitamin D supply?

Vitamin D is also found in a small number of foods such as:

  • Oily fish – such as salmon, sardines, herring, mackerel and fresh tuna
  • Red meat and liver
  • Egg yolks
  • Fortified foods – such as most fat spreads and some breakfast cereals
  • Another source of vitamin D is dietary supplements - your doctor can advise you if you need to take supplements.

How much vitamin D do I need?

  • Babies up to the age of one year need 8.5-10mcg of vitamin D a day
  • Children from the age of one year and adults need 10mcg of vitamin D a day. This includes pregnant and breastfeeding women, and people at risk of vitamin D deficiency.

Am I at risk of sunburn?

Your risk of sunburn depends on two things:

  • How sun-sensitive your skin is
  • How strong the UV rays are you’re exposed to.

Different people will have a different risk of sunburn on the same day, so it’s a good idea to know when your risk is high, so you can protect your skin. During British Summer Time the sun's UV rays are strongest between 11am and 3pm. Be especially careful about protecting your skin from sunburn during these hours by seeking shade, covering up with clothing, a hat and sunglasses and using sunscreen on the parts you can’t cover.

Other things that affect the strength of UV rays are the:

  • Time of year - the highest risk months in the UK are April to September. Near the equator, there are strong UV rays all year round
  • Altitude - UV rays are stronger the higher you go. So skiers and mountaineers can easily get caught out.
  • Cloud cover – over 90% of UV can pass through light cloud
  • Reflection – up to 80% of UV rays are reflected back from snow, 15% from sand, 10% from concrete and up to 30% from water (depending on how choppy it is).

How do I know if my skin’s sun-sensitive?

Anyone can develop skin cancer, but there are some characteristics that mean people are likely to have a higher risk of skin cancer, and need to take more care in the sun. In general people who have one or more of the following are at more risk:

  • Skin that burns easily
  • Light or fair coloured skin, hair, or eyes
  • Lots of moles or freckles
  • A history of sunburn
  • A personal or family history of skin cancer.

People with naturally dark brown or black skin burn less easily and have a lower risk of skin cancer. But people with darker skin can still develop skin cancers, especially types not related to UV, for example on non-pigmented parts of the body like the soles of the feet.