Have you ever lain awake in bed wondering how it is that all plant life on earth does not burn to a crisp shortly after sunrise? All that vegetation quietly growing in full exposure to the relentless sun directly overhead. But nothing burns.
I covered vitamin D and the effects of sunlight in previous posts but there’s one more sun-related issue I feel compelled to mention, and it relates to the above question. The answer, in a word, is carotenoids. Plants have their own built-in protection mechanism which they kindly bestow on us when we eat them. It is a beautiful example of the unified, circular nature of life, of which we are an integral part.
Carotenoids are plant chemicals which take the form of an orange pigment, so foods which contain them are easily identifiable: sweet potato, carrots, bell peppers, pumpkin, squash, cantaloupe melon, mango and apricots are fine examples. Less identifiable are the carotenoid-rich dark leafy greens whose green pigment predominates: kale, spinach, greens and the like. There are many different types, the best known being beta carotene (carrots), lycopene (tomatoes), alpha carotene (pumpkin and carrots), lutein and zeaxanthin (kale and spinach). Carotenoids protect the plant from damage from UV light and this protection is attributed to their antioxidant properties: they are able to absorb the harmful oxidative chemicals produced during photosynthesis, the process whereby plants make energy from sunlight.
Both animal and human studies have consistently shown that eating carotenoid-rich foods protects against damage from ultraviolet irradiation from the sun. In humans sun damage causes not only burning (known as erythema) but also premature ageing of the skin and cancer. A diet rich in lycopene in particular has been found to significantly lower the risk of burns to the skin.
So carotenoids are effective against burning – what about skin cancer? Well, animal studies have confirmed that carotenoids protect against skin cancer, but as far as humans go we don’t know. Randomised, controlled trials of humans are lacking, not surprisingly.
Animal studies are good enough for me. Clearly we have to exercise common sense when it comes to sun exposure, but we should equally ensure a regular supply of dietary carotenoids, and not just the day before the summer holidays. Studies which have demonstrated the protective effects of carotenoids have also shown that they have to be consumed regularly, in high amounts over weeks and months, not just days. The odd tomato or carrot is not going to cut it. The carotenoids that you eat from fruit and vegetables are distributed around the body, with higher concentrations found in the skin and the eye. Sometimes you can tell when you’ve eaten a lot as they affect skin colour, making it appear more yellow.
It is possible – just possible – that the alarming increase in skin cancer rates in the UK and Ireland is related to the equally alarming low level of fruits and vegetables, and therefore carotenoids, in the average diet. Data from the latest National Diet and Nutrition Survey for adults reveal that in Great Britain just 7% of girls and 22% of boys aged 11 to 18 years, and 33% of women and 37% of men are meeting the five-a-day guidelines for fruit and vegetable consumption. With so little carotenoid consumption we really are at risk, especially the fair-skinned whose defences are already down.
We are regularly exhorted to slather ourselves in sunscreen to protect ourselves from the sun’s rays, but never to eat more carotenoids. These sunscreens contain an unnerving mix of chemicals whose safety is always the subject of doubt and which even within the scientific community remains a matter of opinion.
So get eating your carotenoids now. And here’s an extra tip. Carotenoids are fat soluble so put some butter on those carrots, and extra virgin olive oil on those tomatoes to improve your absorption. Cooked is better than raw, as the cooking process releases the carotenoids from the vegetable, making them more readily available.
Stahl, W. & Sies, H. (2002) Carotenoids and protection against solar UV radiation. Journal of Pharmacological and Biophysical Research, 15(5).
Stahl, W. et al (2000) Carotenoids and carotenoids plus vitamin E protect against ultraviolet light-induced erythema in humans. American Journal of Clinical Nutrition, 71(3):795-798.
Bates, B., Lennox, A. Swan, G. (eds) 2010 National diet and nutrition survey: headline results for year 1 of the rolling programme (2008/2009). Food Standards Agency.
Sies, H. & Stahl, W. (2004) Nutritional protection against skin damage from sunlight. Annual Review of Nutrition, 24:173-200.
Jensen, J.D., Wing, G.J. & Dellavalle, R.P. (2010) Nutrition and melanoma prevention. Clinics in Dermatology, 28(6):644-649.
Well I did not know any of that but I am eating some grated carrot as part of my salad – though I was surpised that cooked is bettter than raw. It is usually seems the other way around.
As the French say so picturesquely ‘je me coucherai un peu moins con ce soir’.
Raw is often more nutritious, but not in this case – cooking releases the carotenoids making them more readily available. But don’t let that stop you grating carrot on your salad. Or quoting French randomly!