Skin cancers are the commonest cancers globally and by far the majority of these ubiquitous tumours are caused by excessive exposure to the sun.

The sun's ultraviolet rays (UVR) are those responsible for inducing several pre-malignant processes in the skin. Not only do they damage DNA directly but they also cause inflammation, excess free radical production and immunosuppression. These factors combine to form a tumourigenic cocktail that increases the risk for melanoma and non-melanoma skin cancers.

In spite of their potentially damaging effects UVRs also provide crucial health benefits; therefore it is important that the human skin is exposed to the sun for limited periods of time. The most important of these benefits is UVB rays' involvement in the production of vitamin D from dehydrocholesterol in the deep layers of the skin.

There is also evidence that a lack of exposure to the sun's rays is a significant factor in the development of diseases such as multiple sclerosis and certain malignancies other than skin cancer.

It is worth noting that the human body does attempt to prevent the accumulation of radiation damage and does so by initiating repair mechanisms at relatively low levels of radiation exposure.

These processes involve both intrinsic and extrinsic (plant derived) antioxidants, enzymes and other protective plant based compounds and work in the following ways:

1. Activation of mechanisms that counter free radical damage and oxidative stress.

2. Acceleration of programmed cell death (apoptosis) of pre-cancerous cells.

3. Activation of DNA repair mechanisms at low levels of radiation exposure.

There is a dichotomy in relation to UVR. On the one hand, in order to sustain normal physiological processes, we need a certain amount of exposure to the sun. However, if we are exposed to excessive amounts of UVR and have inadequate protective biological processes, we increase our risk for several different types of skin cancer.

It seems obvious that, as humans have lived for eons with constant exposure to the sun, our bodies would have adapted protective strategies to counter the damaging effects of UVR while still obtaining the benefits thereof. We now know what some of these strategies are but, in order to understand how to enhance them, we need to take a look back over thousands of years at the vital role nutrient dense plant foods play in this regard.

Only a few thousand years ago our hunter-gatherer ancestors roamed, more or less naked, predominantly in the sun-drenched regions of the planet. Thanks to a more extensive ozone layer, they were probably exposed to slightly lower doses of UV radiation per unit time than we are today. However they undoubtedly spent long periods of time in the sun while they hunted and collected plant foods. They also had dark skins that gave them an extra measure (but by no means complete) of protection against excessive UVR exposure. There is evidence that they lived well into their sixties and were therefore subject to significant UVR exposure for several decades.

Protective phytonutrients

The key to our forefathers' success in countering UVR damage was their consumption of a diet rich in phytonutrients. Owing to their active lifestyle, hunter-gatherer communities consumed a high calorific diet. The difference between their high calorie diet and a contemporary high calorie diet is that the former consisted largely of richly flavoured (spicy), phytonutrient-dense plant foods while the modern diet is dominated by relatively bland nutrient deficient plant foods.

The nutritional characteristics of the plants that hunter-gatherers consumed were different to ours in that they had far higher phytonutrient/calorie ratios to the plants we eat today. Those that are available nowadays are generally energy dense plant foods with much lower phytonutrient/calorie ratios.

There are two reasons for this. Firstly, we eat many grain based foods that have very high carbohydrate levels and relatively low phytonutrient levels. Secondly, over the centuries, we have bred varieties of most of our grains, fruit and vegetables that are far bigger, sweeter and starchier than they were in their natural state.

Add to this modern chemical farming methods and we now have plant foods with very low phytonutrient/calorie ratios that consist primarily of water and carbohydrates. These provide far fewer protective compounds than they did several thousand years ago. This translates into reduced intake of phytonutrients that, in adequate amounts, could protect us against UVR and other carcinogenic environmental factors.

The only food categories that have more or less escaped the plant breeders' attentions are the spices. Spices are the plant foods closest to those that our ancestors ate. They have extremely high phytonutrient/calorie ratios and contain large concentrations of a wide variety of powerful antioxidants and other protective nutrients.

Recent scientific evidence has shown that several spices contain compounds that are very effective in countering UVR damage to the skin. These molecules possess the ability to act as direct and indirect antioxidants. They have anti-inflammatory and immunomodulatory properties and can activate genes that control lasting protective processes against UVR damage. Scientists working in this field have also noted that multiple antioxidant compounds (found in phytonutrient-rich plants) have a better protective effect than high doses of single antioxidant supplements.

Spices known to have specific protective effects against radiation damage are:

Turmeric contains the anti-inflammatory, antioxidant, curcumin that has remarkable cancer fighting abilities against several cancers including melanomas.

Mustard contains sulphorafane, a non-antioxidant compound also found in cruciferous plants such as broccoli. Sulphorafane works by activating the body's intrinsic cellular defenses against UVR and has been shown counter skin malignancies when used both internally and topically.

Curcumin and sulphoraphane are only two of the spice-based compounds that are currently being studied as possible treatments for a range of skin and other cancers. However, as spices provide a wide array of antioxidant and other protective compounds, it is highly likely that there are many more of them that can help us contain skin cancers as they undoubtedly did for our hunter-gatherer ancestors.

A combination of selective plant breeding, modern agricultural methods and poor dietary habits means that, without an injection into our diets of a significant quantity and variety of phytonutrient-rich foods such as spices, it almost impossible to obtain the optimum quantities of protective plant compounds. Until we do so we will continue to see a rise in the incidence of skin cancers and other malignancies.