维生素A摄入量增加与降低皮肤癌风险有关 Higher vitamin A intake linked to lower skin cancer risk

与那些摄入少量富含维生素A的食物和补充剂的人相比,饮食中含有高水平维生素A的人患上第二常见类型的皮肤癌的风险降低了17%。

根据布朗大学的研究人员的说法,他在分析了两项长期观察研究的数据后发现了这一发现。

皮肤鳞状细胞癌是皮肤白皙的人中第二常见的皮肤癌。已知维生素A对皮肤细胞的健康生长和成熟至关重要,但之前关于其降低皮肤癌风险的有效性的研究结果参差不齐,布朗的皮肤病学和流行病学副教授Eunyoung Cho说。

“我们的研究提供了另一个理由来吃大量的水果和蔬菜作为健康饮食的一部分,”Cho说,她也是布莱根妇女医院的流行病学副研究员。 “皮肤癌,包括鳞状细胞癌,很难预防,但这项研究表明,除了戴防晒霜和减少阳光照射外,吃富含维生素A的健康饮食可能是降低风险的一种方法。”

该研究结果于7月31日星期三在美国医学会皮肤病学杂志上发表。

Cho领导的研究小组研究了两项大型长期观察研究的参与者的饮食和皮肤癌结果:护士健康研究,其中包括1984年至2012年的121,700名美国女性,以及卫生专业人员随访研究从1986年到2012年,其中有51,529名美国男子。

在这两项研究中,约有123,000名参与者为白人(因此患有皮肤癌的风险很大),既往没有癌症病史,多次完成饮食报告。在该团队随后的分析中包括的这些个体中,共报告了3,978例鳞状细胞癌,并在24或26年的随访期内进行了验证。

两项研究还向参与者询问了头发的颜色,他们一生中接受过的严重晒伤的次数以及皮肤癌的任何家族史,研究人员对这些和其他因素进行了调整。然而,这些研究没有向参与者询问他们是否避免中午日晒,这被认为是皮肤癌的主要危险因素。

根据维生素A摄入量将研究参与者分为五类,研究人员发现,平均每日总维生素A摄入量最高的人群患皮肤癌的可能性比总维生素A最低的人群低17%。一个摄入量。

最高类别的人报告平均每天摄入相当于一个中等烤制的甘薯或两个大胡萝卜的维生素A的量。最低类别的人报告说每日平均摄入维生素A的量相当于三分之一的甘薯薯条或一个小胡萝卜,这仍高于美国推荐的维生素A膳食摄入量。

该团队还发现,大部分维生素A来自参与者的饮食,特别是来自水果和蔬菜,而不是来自动物性食物或维生素补充剂。基于植物的维生素A来源不仅包括甘薯和胡萝卜,还包括绿叶蔬菜和水果,如杏子和哈密瓜。牛奶,某些类型的鱼和肝脏是动物性维生素A的丰富来源。

Cho警告说,过多的维生素A,特别是补充剂和动物源,会导致恶心,肝脏毒性,骨质疏松症和髋部骨折的风险增加,甚至出生缺陷。她补充说,高含量植物维生素A的副作用很小。

研究人员还发现,摄入高水平的其他类似维生素A的植物性色素 – 如西红柿和西瓜中常见的番茄红素 – 与降低患皮肤癌的风险有关。

因为分析的基础是调查大量人们关于他们吃的食物并观察他们是否患有皮肤癌的研究,而不是随机临床试验,因此无法确定因果关系。另一个因素可能导致了这些差异 – 例如,摄入更多维生素A的人也倾向于少喝酒。

作为下一步,Cho想进行一项临床试验,看看维生素A补充剂是否可以预防鳞状细胞癌。然而,她补充说,进行膳食临床试验在技术层面上是非常具有挑战性的,因为确保参与者实际上坚持饮食。

“如果不能进行临床试验,那么像这样的大规模前瞻性研究是研究饮食的最佳选择,”Cho说。

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NEWS RELEASE 

Higher vitamin A intake linked to lower skin cancer risk

BROWN UNIVERSITY

PROVIDENCE, R.I. [Brown University] — People whose diets included high levels of vitamin A had a 17 percent reduction in risk for getting the second-most-common type of skin cancer, as compared to those who ate modest amounts of foods and supplements rich in vitamin A.

That’s according to researchers from Brown University, who unearthed that finding after analyzing data from two long-term observational studies.

Cutaneous squamous cell carcinoma is the second-most-common type of skin cancer among people with fair skin. Vitamin A is known to be essential for the healthy growth and maturation of skin cells, but prior studies on its effectiveness in reducing skin cancer risk have been mixed, said Eunyoung Cho, an associate professor of dermatology and epidemiology at Brown.

“Our study provides another reason to eat lots of fruits and vegetables as part of a healthy diet,” said Cho, who is also an associate epidemiologist at Brigham and Women’s Hospital. “Skin cancer, including squamous cell carcinoma, is hard to prevent, but this study suggests that eating a healthy diet rich in vitamin A may be a way to reduce your risk, in addition to wearing sunscreen and reducing sun exposure.”

The findings were published on Wednesday, July 31, in the Journal of the American Medical Association Dermatology.

The research team led by Cho looked at the diet and skin cancer results of participants in two large, long-term observational studies: the Nurses’ Health Study, which followed 121,700 U.S. women from 1984 to 2012, and the Health Professionals Follow-Up Study, which followed 51,529 U.S. men from 1986 to 2012.

Between the two studies, some 123,000 participants were white (and thus had significant risk of developing skin cancer), had no prior history of cancer and completed the dietary reports multiple times. Among these individuals included in the team’s subsequent analysis, a total of 3,978 cases of squamous cell carcinoma were reported and verified within the 24- or 26-year follow-up periods.

Both studies also asked the participants about hair color, the number of severe sunburns they had received in their lifetime and any family history of skin cancer, and the researchers adjusted for these and other factors. The studies did not, however, ask participants about their avoidance of mid-day sun, known to be a major risk factor for skin cancer.

After grouping the study participants into five categories by vitamin A intake levels, the researchers found that people in the category with the highest average daily total vitamin A intake were 17 percent less likely to get skin cancer than those in the category with the lowest total vitamin A intake.

Those in the highest category reported eating on average the amount of vitamin A equivalent to one medium baked sweet potato or two large carrots each day. Those in the lowest category reported eating a daily average amount of vitamin A equivalent to one-third cup of sweet potato fries or one small carrot, which is still above the U.S. Recommended Dietary Allowance of vitamin A.

The team also found that the majority of vitamin A came from the participants’ diets, particularly from fruits and vegetables, rather than from animal-based foods or vitamin supplements. Plant-based sources of vitamin A include not only sweet potatoes and carrots, but leafy green vegetables and fruits like apricots and cantaloupe. Milk, some types of fish and liver are rich sources of animal-based vitamin A.

Cho cautioned that too much vitamin A, particularly from supplements and animal sources, can lead to nausea, liver toxicity, increased risk of osteoporosis and hip fracture, and even birth defects. Side effects from high levels of plant-based vitamin A are minimal, she added.

The researchers also found that eating high levels of other plant-based pigments similar to vitamin A — such as lycopene, commonly found in tomatoes and watermelon — was associated with decreased risk of skin cancer.

Because the analysis was based on studies surveying a large number of people about the foods they ate and observing whether or not they got skin cancer, rather than a randomized clinical trial, it cannot establish cause and effect. It’s possible that another factor may have led to the differences — such as the fact that people who consumed more vitamin A also tended to drink less alcohol.

As a next step, Cho would like to conduct a clinical trial to see if vitamin A supplements can prevent squamous cell carcinoma. However, she added, conducting a dietary clinical trial is quite challenging on a technical level, as is ensuring that participants actually stick to the diet.

“If a clinical trial cannot be done, then a large-scale prospective study like this is the best alternative for studying diet,” Cho said.

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Other authors on the paper from Brown University include Dr. Jongwoo Kim, now at Inje University Sanggye-Paik Hospital in South Korea; Min Kyung Park; Wen-Qing Li and Dr. Abrar Qureshi.

The research was supported by the National Institutes of Health (grant numbers CA186107, CA87969, CA167552 and CA198216) as well as a research career development award from the Dermatology Foundation.

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