Those with a higher dietary intake of vitamin A than what is officially recommended are 17 percent less likely to develop the second-most common skin cancer compared with those who get limited quantities of the nutrient, according to a study from Brown University in the USA. Beware that vitamin A is found in different forms in various foods and that one of these forms (retinol) can be overdosed.
There are two main types of common skin cancer: basal cell carcinoma and squamous cell carcinoma. The most common sign is a spot or bump on the skin. Regular skin cancer is very easy to treat, and this disease should not be confused with melanoma. People with fair skin are more likely to develop regular skin cancer because their skin is more vulnerable to the ultraviolet sunrays. Other underlying factors include tanning beds, certain chemical compounds, viruses, and genetics. The best way to prevent skin cancer is to avoid sunburns. However, diet also appears to play a role
Basal cell carcinoma – is the most common type of skin cancer. It is relatively harmless but requires treatment to prevent the disease from spreading to its surroundings and destroying the skin tissue. The cancer itself is typically located on the face, the upper part of the chest, and the back. The disease usually begins as a dome-shaped bump, a red, scaly patch of skin, or a wound that does not heal and has a well-defined boundary. It grows slowly and does not spread.
Squamous cell carcinoma – is less common and relatively harmless. The cancer is often located in a sun-exposed area like the face and hands. The disease starts as scaly eczema that eventually develops into a tumor, in some cases with a wound. This form of cancer is more aggressive than basal cell carcinoma, and the disease may become dangerous if it is not treated in time.
Vitamin A is important for skin cells and as an antioxidant
Squamous cell carcinoma is the second-most common form of skin cancer among fair-skinned people. The skin pigmentation – which is the dark colorant melanin – has a protective effect, and because dark-skinned people have much more skin pigment, they are much less likely to develop skin cancer. It is a good idea to slowly adapt to the sun in the early spring and gradually build a tan, so your skin is better protected. Also, sun exposure helps synthesize the essential vitamin D. What you eat also makes a difference.
Vitamin A is known to be of importance for normal, healthy growth and maturation of skin cells. Vitamin A is also an essential antioxidant that protects against oxidative stress caused by excess free radicals, which are aggressive molecules that attack our cells. The number of free radicals is increased by factors such as sunburns, ageing, poisoning, and other stress factors. Earlier studies have show different outcome in terms of vitamin A’s ability to lower the risk of skin cancer. A possible explanation for this could be that vitamin A from plant and animal sources occur in different forms, as shown below
Pure vitamin A from animal sources
Precursor of vitamin A from plant sources
|Found in animal sources like cod liver oil, liver, liver pate, butter, cheese, egg yolks, and oily fish||Found in green/read/yellow vegetables like sweet potatoes, carrots, tomato, rosehip, parsley, kale, spinach, and bell pepper|
Stored in the liver and fatty tissue for later.
Zinc is required to release retinol from the liver.
The body stores retinol for longer periods.
Is converted into retinol as needed in the intestinal mucosa.
The body does not store it.
A very powerful antioxidant
|The strongest vitamin A source.
12 times stronger than beta-carotene.
Possible to overdose.
|The weakest form of vitamin A.
Our need for beta-carotene is correspondingly greater.
Not possible to overdose and is therefore safer for supplementation.
Vitamin A lowers the risk of squamous cell carcinoma by 17 percent
The scientists from Brown University looked closer at the relation between diet habits and the development of skin cancer by analyzing two long-term studies: “Nurses Health Study” (that followed 121,700 American women from 1984 to 2012) and “Health Professionals’ Follow-Up Study” (that monitored 51,529 American men from 1986 to 2012).
Around 123,000 people with light skin (increased risk of skin cancer) participated in the two studies. They had no previous history of skin cancer, and in the course of the studies they filled in several diet questionnaires. During the follow-up period that lasted between 24 and 26 years, 3,978 of the participants developed squamous cell carcinoma. The researchers looked at hair color, the number of severe sunburns throughout the participants’ lives, and family history of skin cancer. After that, they adjusted for confounding factors.
Then all study participants were divided into five groups, ranked according to their dietary intake of vitamin A.
The scientists observed that the group with the highest vitamin A intake had a 17 percent lower risk of developing skin cancer. Those who got most vitamin A reported that they consumed 1-2 sweet potatoes or two large carrots daily on average, which increased their vitamin A intake to a level that is beyond the official guidelines.
The participants with the lowest vitamin A intake reported that, on average, they got around one third of a serving of sweet potato or carrot daily. This squares with the official recommendations, but their vitamin A intake was far below the group that got most.
What the Brown University research team also found was that the participants mainly got vitamin A from vegetable sources like fruit and greens rather than animal sources and vitamin supplements.
It is worth making a note of the fact that vitamin A from vegetable sources (beta-carotene) also has a powerful antioxidant function and protects the skin against oxidative stress from the sun’s ultraviolet rays.
The scientists recommend including fruit and vegetables with a high beta-carotene content as part of a healthy diet.
It is possible to get an overdose of pure vitamin A in the form of retinol, although this rarely happens. Also, toxic levels are not reached until the liver reaches its retinol saturation point and you continue to ingest large quantities of retinol after that.
The new study also showed that other plant-based antioxidants are associated with a lowered risk of skin cancer, including lycopene (tomatoes and water melon).
In their next study, the scientists plan to conduct a clinical trial to see if vitamin A supplementation can prevent squamous cell carcinoma. As they showed with the current study, it takes more vitamin A than the official recommendations to obtain a protective effect against skin cancer.
Recommended Intake (RI) level
Adults: 11 years and older: 800 micrograms/RE (= retinol equivalents)
Children: 1-10 years: 400 micrograms/RE (= retinol equivalents)
1 RE = 1 microgram retinol = 12 micrograms of beta-carotene
Vitamin A supplements and upper safe intake limit
Always take supplements with a meal. The fat in the meal increases the absorption of retinol, which is lipid-soluble.
Transient symptoms such as nausea may occur if supplements are taken on an empty stomach.
The maximum daily dose for vitamin A is 3,000 RE. Post-menopausal women should not exceed 1,500 RE daily, as larger quantities for longer periods of time increases their risk of osteoporosis. Retinol poisoning is only experienced with doses that exceed 15 milligrams (15,000 RE) daily.
Pregnant women should not eat pure liver or take retinol supplements other than the vitamin A that is found in regular vitamin pills for pregnancy. Too much vitamin A (retinol) may harm the fetus. Beta-carotene, on the other hand, cannot be overdosed.
Jongwoo Kim et al. Association of Vitamin A Intake With Cutaneous Squamous Cell Carcinoma Risk in the United States. JAMA Dermatology, 2019
Brown University. “Higher vitamin A intake linked to lower skin cancer risk”. ScienceDaily 2019
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