天黑请关灯：夜间灯光越亮，乳腺癌、超重、肥胖的风险越高

　　在2010年发表的癌症原因与控制研究中，第一次分析了人口环境暴露与夜间灯光之间的相关性，以及世界各地164位女性的几种癌症发生率。该研究基于1996～2002年的数据并得出结论：乳腺癌的发病率与夜间灯光有显著相关性，而其他癌症类型未见此相关性。然而，一个悬而未决的问题仍然是，该趋势对最近的数据是否也是如此。

　　2015年6月，以色列海法大学根据2002～2012年国际癌症研究机构（IARC）全球癌症数据库（GLOBOCAN）、美国国防气象卫星计划（DMSP）、世界银行数据库获得的信息，重新分析了全球180个国家的乳腺癌发病率与夜间灯光的相关性强度，并考虑了几个国家级预测因素，包括出生率、城市人口百分比、人均GDP和用电量。考虑到潜在不同延迟期，还比较乳腺癌年龄标准化率与不同年度测得的夜间灯光。与2002年乳腺癌数据的分析结果相比，排除潜在混杂因素后，2012年乳腺癌与夜间灯光之间的相关性似乎已经整体减弱，未见统计学意义（t＜0.3，P＞0.5）。然而，当整个国家样本被分解为类似发达国家的地理集群时，乳腺癌与夜间灯光的正相关性重新出现统计学意义（t＞2.2，P＜0.01）。原因之一可能为世界范围内乳腺癌年龄标准化率存在65～85%的变异性，并取决于模型类型。虽然本分析再次证实了乳腺癌与夜间灯光的正相关性，但是近年来这种相关性似乎存在区域分歧，西欧国家可见此相关性水平最高，而东南亚和海湾国家表现为夜间灯光相对较亮时乳腺癌率相对较低。这种区域分层可能是由于额外的保护机制减少了乳腺癌的风险，例如当地的饮食和生活方式。

　　2016年5月、12月，英国《自然》旗下《国际肥胖杂志》、爱思唯尔旗下《整体环境科学》发表以色列海法大学、美国康涅狄格大学、美国康涅狄格儿童医疗中心的研究报告，通过分析夜间照明卫星图像发现：夜间灯光亮度与乳腺癌、超重和肥胖存在相关性。

　　该研究利用美国国防气象卫星计划（DMSP）的有关资料，查看夜间照明卫星图像，同时对照分析世界卫生组织发布的超重和肥胖率，发现夜间灯光越亮的地区，超重和肥胖的比例越大（t＞1.97，P＜0.05）。

　　此外，夜间灯光强弱也同乳腺癌发病率存在相关性，灯光越亮、持续时间越长的城市，其女性乳腺癌发病率也越高。在美国康涅狄格州，考虑若干潜在混杂因素后，夜间灯光亮度最高与最低的地区相比，乳腺癌风险增加63%（风险比：1.63，95%置信区间：1.41～1.89）。夜间灯光亮度与乳腺癌发病的相关性随年龄增加而减弱，在绝经前女性中的相关性最强。由于用电照亮夜晚是工业化的标志，故乳腺癌风险在工业化地区较高，而在发展中地区增加较快。

　　该研究作者认为，灯光影响人体生成褪黑素，进而打乱人体生物钟，带来生理和行为上的变化，从而导致肥胖。正常情况下，人体内褪黑激素在一天不同时段起伏变化，在夜间达到峰值水平，白天时会下降。

　　在既往研究中，荷兰科学家在对小鼠进行的实验中发现，让小鼠每天24小时处于光照照射下，即使与其他小鼠吃得一样多、运动一样多，其脂肪量也会增加50%。

　　因此，作者建议，在城市，尤其是大城市生活的人，要尽量避免灯光带来的负面影响，如安装遮光较好的窗帘减少路灯等灯光照射量，晚上室内灯光不要太亮，睡前减少看屏幕的时间等。

Sci Total Environ. 2016 Dec 1;572:1020-1024.

Light at night and breast cancer incidence in Connecticut: An ecological study of age group effects.

Portnov BA, Stevens RG, Samociuk H, Wakefield D, Gregorio DI.

University of Haifa, Haifa, Israel; University of Connecticut, Farmington, CT, United States; Connecticut Children's Medical Center, Hartford, CT, United States.

Highlights

• Breast cancer risk is high in the industrialized world and rising rapidly in the developing world.

• There is no scientific consensus on the primary cause, unlike for most other cancers.

• A hallmark of industrialization is the increasing use of electricity to light the night.

• Light at night is a new exposure in the human environment that can disrupt circadian rhythmicity.

• This excessive lighting may be part of the explanation for breast cancer pandemic.

The aim of this study was to test the prediction that within the state of Connecticut, USA, communities with high nighttime outdoor light level would have higher breast cancer incidence rates. Breast cancer cases were identified from the Connecticut Tumor Registry, the oldest within the United States, for years 2005 and 2009 and geocoded to the 829 census tracts in the state. Nighttime light level (LAN) was obtained from the Defense Meteorological Satellite Program (DMSP), 1996/97 satellite image, providing a 10-year lag. Regression models were used incorporating the LAN levels and census level data on potential confounders for the whole female population of the state, and for separate age groups. Light level emerged as a significant predictor of breast cancer incidence. After taking account of several potential confounders, the excess risk in the highest LAN level census tracts compared to the lowest was about 63% (RR=1.63; 95% CI=1.41, 1.89). The association of LAN with breast cancer incidence weakened with age; the association was strongest among premenopausal women.

KEYWORDS: Breast cancer; Circadian disruption; Ecological study

PMID: 27531467

DOI: 10.1016/j.scitotenv.2016.08.006

Int J Obes (Lond). 2016 May;40(5):815-23.

Does artificial light-at-night exposure contribute to the worldwide obesity pandemic?

Rybnikova NA, Haim A, Portnov BA.

University of Haifa, Haifa, Israel.

BACKGROUND: Worldwide overweight and obesity rates are on the rise, with about 1,900 billion adults being defined as overweight and about 600 million adults being defined as obese by the World Health Organization (WHO). Increasing exposure to artificial light-at-night (ALAN) may influence body mass, by suppression of melatonin production and disruption of daily rhythms, resulting in physiological or behavioral changes in the human body, and may thus become a driving force behind worldwide overweight and obesity pandemic.

METHODS: We analyzed most recent satellite images of night time illumination, available from the US Defense Meteorological Satellite Program (DMSP), combining them with country-level data on female and male overweight and obesity prevalence rates, reported by the WHO. The study aims to identify and measure the strength of association between ALAN and country-wide overweight and obesity rates, controlling for per capita GDP, level of urbanization, birth rate, food consumption and regional differences.

RESULTS: ALAN emerged as a statistically significant and positive predictor of overweight and obesity (t>1.97; P<0.05), helping to explain, together with other factors, about 70% of the observed variation of overweight and obesity prevalence rates among females and males in more than 80 countries worldwide. Regional differences in the strength of association between ALAN and excessive body mass are also noted.

CONCLUSIONS: This study is the first population-level study that confirms the results of laboratory research and cohort studies in which ALAN was found to be a contributing factor to excessive body mass in humans.

PMID: 26795746

DOI: 10.1038/ijo.2015.255

Chronobiol Int. 2015 Jun;32(6):757-73.

Artificial Light at Night (ALAN) and breast cancer incidence worldwide: A revisit of earlier findings with analysis of current trends.

Rybnikova N, Haim A, Portnov BA.

University of Haifa, Haifa, Israel.

In a study published in Cancer Causes & Control in 2010, Kloog with co-authors tested, apparently for the first time, the association between population-level ambient exposure to artificial light at night (ALAN) and incidence of several cancers in women from 164 countries worldwide. The study was based on 1996-2002 data and concluded that breast cancer (BC) incidence was significantly and positively associated with ALAN, while no such association was revealed for other cancer types. An open question, however, remains whether the trends revealed by Kloog and co-authors were time specific or also hold true for more recent data. Using information obtained from the GLOBOCAN, US-DMSP and World Bank's 2002 and 2012 databases, we reanalyzed the strength of association between BC incidence rates in 180 countries worldwide and ALAN, controlling for several country-level predictors, including birth rates, percent of urban population, per capita GDP and electricity consumption. We also compared BC age-standardized rates (ASRs) with multi-annual ALAN measurements, considering potentially different latency periods. Compared with the results of Kloog et al.'s analysis of the year-2002 BC-data, the association between BC and ALAN appears to have weakened overall, becoming statistically insignificant in the year 2012 after being controlled for potential confounders (t<0.3; p>0.5). However, when the entire sample of countries was disaggregated into geographic clusters of similarly developed countries, a positive BC-ALAN association re-emerged as statistically significant (t>2.2; p<0.01), helping to explain, along with other factors covered by the analysis, about 65-85% of BC ASR variability worldwide, depending on the model type. Although the present analysis reconfirms a positive BC-ALAN association, this association appeared to diverge regionally in recent years, with countries in Western Europe showing the highest levels of such association, while countries in Southeast Asia and Gulf States exhibiting relatively low BC rates against the backdrop of relatively high ALAN levels. This regional stratification may be due to additional protective mechanisms, diminishing BC risks and potentially attributed to the local diet and lifestyles.

KEYWORDS: Age standardized rates; artificial light at night; breast cancer; regional differences; world countries

PMID: 26102518

DOI: 10.3109/07420528.2015.1043369