每日使用防晒霜可减缓中年人皮肤老化

6月3日《内科学年鉴》在线发表的一项针对中青年的随机对照试验结果显示，与随意使用防晒霜者相比，每日使用者4.5年后出现皮肤老化迹象的可能性明显减少，但β-胡萝卜素补充剂似乎对皮肤老化没有影响 (2013;158:781-90)。



澳大利亚昆士兰医学研究院的Maria Celia B. Hughes及其同事称，此前未见到评价防晒霜对人类皮肤老化相关变化的影响的随机研究。澳大利亚楠普拉皮肤癌预防试验是一项评价防晒霜或膳食补充剂对皮肤癌风险、光老化以及光化性角化病发病影响的研究，于1992~1996年共计纳入1,621例成人，评估坚持每日使用防晒霜对皮肤老化进程的预防作用。他们将年龄＜55岁的903例受试者随机分为4组：每日使用广谱防晒霜+30 mg β-胡萝卜素、每日使用广谱防晒霜+安慰补充剂、随意使用防晒霜+30 mg β-胡萝卜素、随意使用防晒霜+安慰补充剂。研究者之所以关注年龄＜55岁的成人，是为了排除衰老对皮肤老化的潜在影响。

研究者根据对受试者手背的感观印象，比较基线(1992年)和4.5年后(1996年)皮肤微形态变化以评估皮肤老化。评估者对各治疗组采用盲法评估。大多数受试者为白人，急性阳光暴露可致90%以上受试者皮肤晒伤。各组受试者表型、阳光暴露和试验前防晒霜使用情况相似。研究期间，各组受试者阳光暴露程度相似，78%的每日使用防晒霜者和76%的随意使用者周末户外时间＜50%。此外，各组受试者采用寻找遮阳处和戴帽子等其他防晒措施的比例也相似。研究结束时，每日使用防晒霜者和随意使用者每周使用防晒霜至少为3~4天的比例分别为77%和33%。

总体上，受试者在基线和研究结束时符合中度光老化标准的比例分别为58%和49%，但在4.5年研究结束时，每日防晒霜使用者出现皮肤老化迹象的比例比随意使用者减少24%，具有统计学显著意义。在校正颈部皮肤晒伤和光老化后，受试者1996年皮肤微形态分级高于1992年，只有每日使用防晒霜者微形态分级未见增加。β-胡萝卜素补充剂组与安慰剂组皮肤老化未见显著差异。

研究者承认该研究存在多方面的局限性，包括结局数据有限，降低了检测中等治疗效果的效能。此外，用于排除β-胡萝卜素对皮肤老化影响的数据也不足。但研究者强调，上述结果具有重要临床意义。即使微形态仅增加1个分级，也与光化性角化症和皮肤癌风险密切相关。因此，化妆品对中年人皮肤变化的有益作用或许也能够减少癌症风险。

该研究由澳大利亚国家卫生与医学研究委员会资助。

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By: HEIDI SPLETE, Internal Medicine News Digital Network

Daily sunscreen users were significantly less likely than discretionary sunscreen users to show signs of skin aging after 4.5 years, according to a study of young and middle-aged adults.

However, beta-carotene supplements appeared to have no effect on skin aging.
 
The findings from the randomized controlled trial were published online June 3 in Annals of Internal Medicine (2013;158:781-90).

"No known randomized studies in humans have evaluated the effect of sunscreen on surface changes associated with skin aging," wrote Maria Celia B. Hughes, MMedSci., of the Queensland Institute of Medical Research, Australia, and her colleagues.

The investigators used data from the Nambour (Australia) Skin Cancer Prevention Trial, in which 1,621 adults were studied from 1992 to 1996 to test the effect of sunscreen use or dietary supplements on skin cancer risk, photoaging, and actinic keratosis development.

To determine whether consistent, daily sunscreen use could prevent progression of skin aging, researchers randomized Nambour study participants under age 55 into four groups: daily use of broad-spectrum sunscreen plus 30 mg of beta-carotene; daily sunscreen use plus a placebo supplement; discretionary sunscreen use plus 30 mg of beta-carotene; and discretionary sunscreen use plus a placebo supplement.

The investigators focused on 903 adults younger than 55 to exclude the potential effects of growing old on participants’ skin aging.

Skin aging was assessed by comparing skin microtopography based on impressions taken of the backs of participants’ hands at baseline in 1992 and 4.5 years later in 1996. Assessors were blinded to the treatment groups.

"Most of the study participants were fair skinned, and more than 90% burned on acute sun exposure," the researchers noted. The groups were similar in terms of phenotype, sun exposure, and pretrial sunscreen use. All groups reported similar amounts of sun exposure during the study period; 78% of daily sunscreen users and 76% of discretionary sunscreen users reported being outdoors for less than 50% of their weekend time. In addition, the use of other sun protection measures, including seeking shade and wearing a hat, was similar among the groups.

By the end of the study, 77% of the daily sunscreen users applied sunscreen at least 3-4 days per week, vs. 33% of the discretionary users.

Overall, 58% of the participants in the current study met criteria for moderate photoaging at baseline in 1992, and 49% met those criteria in 1996. However, at the end of the 4.5-year period, daily sunscreen users were 24% less likely to show signs of skin aging than were discretionary users, a statistically significant difference.

When the odds of having a higher microtopography grade in 1996 than in 1992 were adjusted for sunburns and photoaging of the neck, the researchers noted, "only the daily sunscreen intervention group showed no detectable increase in microtopography grade."

No significant differences in skin aging were seen in participants randomized to beta-carotene vs. placebo.

The study was limited by several factors, including limited outcome data, which reduced the power to detect moderate treatment effects. In addition, the data were insufficient to rule out an effect of beta carotene on skin aging, the researchers noted.

However, "these results have important clinical implications," the researchers said. "A unit increase in microtopography significantly correlates with risk for actinic keratoses and skin cancer." Thus, the cosmetic benefits of reducing skin changes in middle age also may reduce cancer risk.

The National Health and Medical Research Council of Australia funded the study.