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If the sun causes melanoma why is it found on skin not exposed to the sun

By David Coory

My Mum was a fair skinned redhead and sunburned easily, so she stayed out of the sun and also covered her arms and wore stockings every day. Yet when she was 70, she developed a melanoma in her lower leg. The bare skin on her lower leg would have rarely, if ever, felt the warmth of summer sun. So why did Mum get melanoma when she rarely went out in the sun?

We're constantly warned by media to stay out of the sun to avoid melanoma skin cancer, but the feel of warm sunlight on our skin is one of life's free luxuries. For most people it feels instinctively healthy and reduces anxiety and stress. Also, the ultraviolet B (UVB) tanning rays of the sun on our bare skin are our main source of vitamin D3. We now know that optimum blood levels of vitamin D3 offer huge protection against nearly all cancers, and an average 47% protection against melanoma when our blood levels are between 75 and 120 nmol/L, (magnesium also has a vital role in maintaining these high levels). Many people in NZ are as low as 16 nmol/L in winter.

A world review of 57 melanoma studies concluded that, “A high occupational sun exposure seemed to be inversely associated to melanoma.” In other words, those working outdoors in the sun had a lower incidence of melanoma. Also a Queensland study found, “… more instances of melanoma in office workers than people who work outdoors.

The four main types of melanoma

By knowing all the facts, we can reconcile apparent inconsistencies about melanoma. For a start, there are actually four main types of skin melanoma (and several other rare internal types).

Superficial melanoma (about 65%)

The most common type in NZ, found on the fleshy backs and chests of men and lower legs of women. It starts from a mole. Linked to UVA rays and the lack of UVB tanning rays.

Nodular melanoma (about 15%)

A firm pink, red, brown or black bump that can bleed easily and found on the head and neck. These are aggressive, dangerous and can spread quickly. They do not appear linked to excess sun exposure.

Lentigo maligna melanoma (about 10%)

Found on the face, ears or arms after age 50. These are caused by the sun, are slow growing and not associated with mole mutation.

Acral lentiginous melanoma

More common in those with dark skin. Found on the palms of the hands, or soles of the feet or under the nails.
Not sun related.

Melanoma rates per head of population have remained constant for the past 30 years, but better diagnosis gives the impression of an increase. The death rate from melanoma is actually dropping.

The melanoma cases per 100,000 population are Australia 37,
New Zealand 32, Denmark 30, Norway 26, Sweden 23, Switzerland 22, but the worldwide average is only 3. This low rate is mostly due to darker skin and more vitamin D outdoor activity in the sun.

Worldwide, melanoma is highest in countries with populations who have fair skin and mostly indoor lifestyles, and therefore low vitamin D levels. In NZ and Australia our all year round UVA and UVB sun radiation is much higher than northern hemisphere countries.

If you have more than 50 common moles, or had multiple blistering sunburns when young, the risk is 3 times higher than normal. More than 100 moles, 8 times higher and when combined with a family history of melanoma, up to 12 times higher.

To avoid the risk of melanoma

  1. Avoid margarine and seed oils, as these are high in omega 6 and lower cancer immunity.
  2. Australian researchers find 40% less melanoma in those who have a high omega 3 fish diet.
  3. Try to maintain a light tan, or regular sun exposure on bare skin to maintain a high blood level of vitamin D. Then cover up or use a sunscreen to prevent sunburn.
  4. We should not wash with soap immediately after sunbathing, as the vitamin D is still being absorbed from our skin oils and is easily washed off.

The chart below shows the approx time to manufacture two days worth of vitamin D for all skin types. It has now been found that they all manufacture vitamin D at a similar rate.