Environment & Exposome

Alcohol (ethanol, C₂H₅OH) is a Group 1 human carcinogen whose chronic exposure accelerates biological aging through multiple molecular mechanisms. Ethanol is oxidized to acetaldehyde — a reactive intermediate — by alcohol dehydrogenase (ADH), then to acetate by mitochondrial aldehyde dehydrogenase (ALDH2). When impaired — through excess consumption or the ALDH2*2 loss-of-function variant prevalent in East Asian populations — acetaldehyde forms covalent DNA adducts, driving strand breaks, mutations, and genomic instability. Studies of alcohol use disorder (AUD) find approximately 2–4 years of accelerated biological age on DNA-methylation clocks (Horvath, GrimAge), scaling with severity and partially reversing after abstinence (Zindler et al. 2022, Addiction Biology). Mendelian randomization using ADH1B rs1229984 as an instrumental variable shows genetically-predicted higher alcohol exposure causally shortens leukocyte telomere length (Topiwala et al. 2022, Molecular Psychiatry). A 2024 non-linear MR study of 300,000+ UK Biobank participants found no protective threshold against dementia at any consumption level, contradicting the earlier observational J-curve (Zheng et al. 2024, eClinicalMedicine). IARC concluded in 2023 that no safe consumption level for cancer exists, with strongest causal evidence for cancers of the oral cavity, pharynx, larynx, oesophagus, liver, colorectum, and breast (Gapstur et al. 2023, NEJM); ethanol and acetaldehyde are the primary carcinogens, independent of beverage type.

Chronic psychological stress is a sustained state of perceived threat or demand that persistently activates the hypothalamic–pituitary–adrenal (HPA) axis, resulting in prolonged elevation of the glucocorticoid cortisol. Unlike acute stress responses, chronic stress keeps cortisol tonically elevated; immune cells eventually develop glucocorticoid receptor resistance, losing sensitivity to its anti-inflammatory signalling and leaving pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) unrestrained — a state termed inflammaging. Excess cortisol and reactive oxygen species (ROS) also accelerate telomere attrition: Epel et al. (2004, PNAS) found 39 mothers of chronically ill children had telomeres roughly 550 base pairs shorter than 19 controls — roughly one decade of added biological aging — with 48% lower telomerase activity and an inverse correlation with caregiver years (r = −0.40). Converging evidence links chronic stress to epigenetic clock acceleration and increased all-cause mortality, though most studies are cross-sectional; causal direction has not been established in intervention trials. The HPA–telomere–inflammaging triad is regarded as a biologically plausible, empirically supported mechanism of stress-driven healthspan compression, not a fully proven causal pathway.

Endocrine-disrupting chemicals (EDCs) are exogenous substances that interfere with hormone synthesis, transport, receptor binding or metabolism; bisphenol A (BPA) and its structural analogues (BPS, BPF) act primarily as agonists or antagonists at oestrogen receptors (ERα, ERβ) and also interact with androgen and thyroid hormone pathways, while phthalates — plasticisers used widely in food packaging, medical devices and personal-care products — reduce androgen biosynthesis by inhibiting steroidogenic enzymes. Epidemiological associations include earlier puberty onset, reduced sperm quality, polycystic ovary syndrome, type 2 diabetes and obesity, though establishing causality in observational data is complicated by ubiquitous co-exposure and the non-monotonic dose-response curves characteristic of many EDCs. The EU banned BPA from polycarbonate baby bottles in 2011 and adopted a comprehensive ban on intentional BPA use in food-contact materials in December 2024 (Regulation (EU) 2024/3190), with phased transition periods, and applies a group tolerable daily intake for phthalates, but regulatory thresholds remain contested; cumulative mixture risk assessment is not yet standard practice in most jurisdictions.

The exposome is the totality of environmental exposures an individual encounters from conception to death — spanning chemical, physical, biological, lifestyle, and social factors — and was coined by Christopher Wild in 2005 as a conceptual counterpart to the genome. Wild subsequently elaborated three overlapping domains: a general external environment (urban-rural setting, climate, socioeconomic position), a specific external environment (diet, physical activity, tobacco, occupational hazards, pollutants), and an internal environment (metabolic state, microbiome composition, oxidative stress, inflammation). Measuring the exposome requires integrating wearable sensors, biomarkers in blood and urine (adducts, metabolites), geographic exposure data, and multi-omic profiling — an approach called exposomics. Evidence from large epidemiological datasets consistently links chronic exposomic burden to accelerated biological aging via oxidative DNA damage, mitochondrial dysfunction, cellular senescence, and epigenetic clock advancement; a WHO global environmental burden-of-disease analysis (Prüss-Üstün et al., 2016) attributes roughly 24% of all deaths globally to modifiable environmental factors. Associations between specific exposomic components and aging outcomes are well-documented in human cohorts, yet disentangling causal pathways from confounding — and aggregating across thousands of co-occurring exposures simultaneously — remains an active methodological challenge; the field is associational at the aggregate level and still developing causal inference tools.

Green space exposure denotes proximity to or time spent in vegetated environments — urban parks, street trees, or forests — including the Japanese practice of shinrin-yoku (forest bathing). In a 2019 systematic review and meta-analysis of nine longitudinal cohorts (>8 million adults across seven countries), each 0.1 increment in residential Normalised Difference Vegetation Index (NDVI) within a 500 m buffer was associated with a 4% lower all-cause mortality (pooled HR 0.96, 95% CI 0.94–0.97). Mechanisms include lower chronic stress and cortisol, increased physical activity, social cohesion, reduced air pollution and heat exposure, and — for forest environments — inhalation of phytoncides (volatile wood terpenes) that increase natural killer (NK) cell activity and intracellular anti-cancer proteins; the most robust replication is for persistence beyond 7 days, while up-to-30-day persistence comes from smaller Japanese follow-up cohorts. Effects are dose-dependent and strongest for cardiovascular mortality.

Lead, cadmium and inorganic mercury are the heavy metals most consistently associated with chronic low-level human exposure and adverse health outcomes in epidemiological research. Lead enters via ageing drinking-water infrastructure and legacy paint; cadmium accumulates through cigarette smoke, contaminated soil and certain foods; methylmercury is concentrated in large predatory fish through bioaccumulation. Mechanistically, these metals displace essential ions, inhibit enzymatic activity, generate reactive oxygen species and alter DNA methylation patterns — epigenetic effects linked to accelerated biological ageing. NHANES blood-lead studies have reported a continuous dose-response relationship between blood lead levels and all-cause and cardiovascular mortality even at concentrations previously considered safe, contributing to successive downward revisions of reference values.

Indoor air quality (IAQ) refers to the chemical, biological and physical composition of air inside buildings, where adults in industrialised countries spend ~90% of their time. Key pollutants include volatile organic compounds (VOCs) such as formaldehyde, benzene and toluene from furniture, paints, cleaning products and combustion; nitrogen dioxide (NO₂) from gas cooking; and ultrafine particles from cooking, candles and printers. Elevated VOC and CO₂ levels impair higher-order cognition: the 2016 'COGfx' controlled-exposure study found cognitive function scores were 61% higher in low-VOC green-building conditions and 101% higher with enhanced ventilation, compared to conventional offices. Chronic exposure is linked to Sick Building Syndrome, asthma exacerbation and adverse cardiovascular outcomes. The WHO 2010 indoor air quality guidelines set health-based limits for selected pollutants; in Germany, the Umweltbundesamt issues guide and intervention values for indoor VOCs.

Artificial light at night (ALAN) — from street lighting, screens and indoor illumination — suppresses melatonin secretion via intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing melanopsin, which are maximally sensitive to short-wavelength (~480 nm) blue light, thereby delaying or blunting the nocturnal melatonin surge and phase-shifting the master circadian clock in the suprachiasmatic nucleus. Chronic circadian misalignment is linked to impaired immune function, metabolic dysregulation, cardiovascular risk and accelerated epigenetic ageing. Epidemiological research by Erren and colleagues, along with multiple large cohort studies, has identified associations between ALAN exposure and elevated incidence of breast and prostate cancer, possibly through melatonin-mediated effects on cell proliferation. Urbanisation trajectories project continued increases in global ALAN intensity, making the biological effects of outdoor and indoor light environment increasingly relevant to public health.

Microplastics are solid plastic particles smaller than 5 mm, encompassing nanoplastics at the sub-micron scale, originating from the fragmentation of larger plastic debris, synthetic textiles, tyre wear and personal-care products. They have been detected in human blood, placental tissue, breast milk and, in a 2024 NEJM study by Marfella and colleagues, within carotid artery atheromas — patients with detectable plaque microplastics had a significantly higher risk of myocardial infarction, stroke and death over a mean follow-up of approximately 34 months. Proposed mechanisms of harm include local inflammatory responses, endocrine disruption via adsorbed chemical additives such as phthalates and bisphenols, and oxidative stress, though dose-response relationships in humans remain poorly characterised. Clinical significance and safe threshold levels have not yet been established, and no validated reduction strategy exists beyond minimising dietary and inhalation exposure.

Indoor fungal contamination — most often Stachybotrys chartarum, Aspergillus and Penicillium species — develops where building dampness persists, and can release viable spores, hyphal fragments and secondary metabolites called mycotoxins (e.g. aflatoxin B1, ochratoxin A, macrocyclic trichothecenes). The 2009 WHO indoor air quality guidelines on dampness and mould conclude that occupants of damp or mouldy buildings have up to a 75% greater risk of respiratory symptoms and asthma, and that ~13% of childhood asthma in the WHO European Region is attributable to damp housing. Aflatoxin B1 is classified by IARC (Monograph 100F, 2012) as a Group 1 human carcinogen; chronic dietary exposure causes hepatocellular carcinoma, especially in HBV-positive populations. Inhalational toxicological evidence is weaker than dietary, but Stachybotrys trichothecenes are potent protein-synthesis inhibitors implicated in sick-building symptoms. Remediation focuses on eliminating moisture, not biocide treatment.

Environmental noise pollution refers to unwanted sound from road, rail, aircraft and industrial sources. Chronic exposure raises cardiovascular morbidity and mortality through non-auditory mechanisms: nocturnal awakenings fragment sleep, hypothalamic–pituitary–adrenal (HPA) axis activation elevates cortisol and catecholamines, and resulting endothelial dysfunction, oxidative stress and vascular inflammation drive hypertension, ischemic heart disease, heart failure and stroke. The 2018 WHO Environmental Noise Guidelines for the European Region strongly recommend keeping average exposure below 53 dB Lden for road traffic, 54 dB Lden for railway, and 45 dB Lden for aircraft noise; the EU mapping threshold under Directive 2002/49/EC remains 55 dB Lden. The European Environment Agency's 2025 report "Environmental noise in Europe" estimates transport noise causes about 66,000 premature deaths, ~50,000 new cardiovascular disease cases, and ~22,000 new type-2-diabetes cases annually in Europe.

Per- and polyfluoroalkyl substances (PFAS) are a class of thousands of synthetic chemicals characterised by extremely stable carbon-fluorine bonds, resulting in environmental persistence and, for long-chain variants such as PFOA and PFOS, serum half-lives in humans of several years. Exposure routes include contaminated drinking water, food packaging, non-stick cookware and occupational contact; PFAS have been detected in blood and tissue globally, including in remote Arctic populations. Epidemiological evidence links PFAS exposure to suppressed antibody responses to vaccines, dyslipidaemia, thyroid hormone disruption, reduced birthweight and increased risk of kidney and testicular cancers, with mechanistic pathways involving PPAR-alpha activation and nuclear receptor interference. In April 2024 the US EPA finalised the National Primary Drinking Water Regulation, setting enforceable maximum contaminant levels for PFOA and PFOS at 4 parts per trillion in drinking water; in May 2025 EPA retained the 4 ppt MCLs for PFOA and PFOS but announced its intent to rescind the MCLs for PFHxS, PFNA, GenX/HFPO-DA and the Hazard Index mixture limit (which covers PFHxS, GenX, PFNA and PFBS), and extended PFOA/PFOS compliance deadlines by two years; as of May 2026 the rescission proposal remains in rulemaking; the EU is pursuing a parallel restriction under REACH covering entire PFAS groups.

PM2.5 refers to airborne particles with an aerodynamic diameter of 2.5 micrometres or less, arising predominantly from combustion sources — vehicle exhaust, power generation, wood burning and industrial processes — as well as secondary formation from gaseous precursors such as sulphur dioxide and nitrogen oxides. Their small size allows deep deposition in the alveolar region and translocation into systemic circulation, where they trigger oxidative stress, endothelial dysfunction and inflammatory cytokine release; carriers of the APOE ε4 allele may face heightened neurological risk through blood-brain barrier penetration. Dose-response analyses by Pope, Burnett and colleagues in large American cohorts have demonstrated continuous associations between long-term PM2.5 exposure and all-cause, cardiovascular and lung-cancer mortality without an apparent safe threshold. The WHO 2021 Air Quality Guidelines tightened the recommended annual mean limit to 5 µg/m³ — a level most European and North American cities still exceed.

Radon-222 is a colourless, odourless, naturally occurring radioactive noble gas formed by uranium-238 decay in soils and rocks; it accumulates in basements and ground-floor rooms of poorly ventilated buildings. Inhaled radon progeny (²¹⁸Po, ²¹⁴Po) deposit alpha-emitting particles in bronchial epithelium, causing the DNA damage that drives lung cancer. Radon is the second leading cause of lung cancer overall (after tobacco) and the leading cause in never-smokers. A 2005 pooled analysis of 13 European case-control studies (7,148 cases) showed an 8% (95% CI 3–16%) increase in lung-cancer risk per 100 Bq/m³ long-term residential exposure. The WHO 2009 handbook recommends a reference level of 100 Bq/m³, not exceeding 300 Bq/m³. Germany's Strahlenschutzgesetz (StrlSchG, in force 2018) sets a 300 Bq/m³ reference value for dwellings and workplaces. Mitigation: sub-slab depressurisation, sealing, increased ventilation.

Shift work — any schedule displacing working hours outside the conventional 07:00–18:00 window, including fixed night shifts and rotating patterns — chronically misaligns behavioral cycles (sleep, feeding, activity) with the endogenous ~24-hour circadian clock governed by the suprachiasmatic nucleus (SCN). Nocturnal light suppresses melatonin, inverts the cortisol rhythm, and shifts meal timing into biologically nocturnal hours, creating internal desynchrony between central and peripheral clocks. A controlled forced-desynchrony protocol (Scheer et al., PNAS 2009) showed that even a few days of misalignment elevated mean arterial pressure, raised postprandial glucose and insulin, and lowered leptin in healthy adults — changes corresponding to prediabetes and hypertension trajectories if sustained. In the UK Biobank cohort (Yang et al., JAHA 2022; n ≈ 36,900), hypertensive participants who worked night shifts usually or always had a 16% higher risk of cardiometabolic multimorbidity (concurrent diabetes, coronary heart disease, or stroke) versus day workers. The IARC classified night shift work as a Group 2A probable human carcinogen in 2007 (Monograph 98), reaffirmed in 2019 (Monograph 124), citing limited epidemiological signals for breast, prostate, and colorectal cancers plus mechanistic evidence from animal models. Cancer causation in humans remains associational; the metabolic and cardiovascular burden from circadian disruption is mechanistically well-supported and directly relevant to accelerated aging phenotypes.

Social determinants of health (SDoH) are the non-medical conditions in which people are born, grow, live, work and age — income, education, employment quality, housing, neighbourhood, social network, early-childhood development and access to services — that shape health outcomes and inequities. The WHO Commission on Social Determinants of Health (CSDH, 2008, chaired by Michael Marmot) framed inequities in power, money and resources as the 'causes of the causes' of disease. The WHO estimates SDoH account for 30–55% of health outcomes, exceeding the contribution of clinical care. In England, the Marmot Review 10 Years On (2020) documented stalled life expectancy and a widening gradient: between 2016-18, men in the most deprived decile lived ~9.5 years (women ~7.7 years) less than those in the least deprived, and the gap in healthy life expectancy at birth was ~19 years for both sexes (ONS). In Germany, the GISD-based analysis by Michalski et al. (2022) reports a life-expectancy gap of ~6.0 years for men and ~3.2 years for women between districts in the lowest and highest deprivation deciles (2015-17 data).

Tobacco smoking is one of the strongest known modifiable accelerators of biological aging, acting through at least three converging mechanisms: epigenetic reprogramming via altered DNA methylation patterns, oxidative-stress-driven telomere attrition, and chronic low-grade inflammation promoting vascular and tissue senescence. In respiratory tissues, Wu et al. (2019, Clinical Epigenetics) found an average epigenetic age excess of 4.9 years in airway epithelium and 4.3 years in lung parenchyma among smokers; airway acceleration was partly reversible after cessation, whereas lung parenchyma acceleration persisted. Gao et al. (2016, Oncotarget) identified 66 of 150 smoking-associated CpG methylation sites that also overlapped with age-associated CpGs — though that study found no significant association between self-reported smoking status per se and overall epigenetic age acceleration, pointing to complexity in the methylation-aging relationship. The GrimAge clock (Lu et al. 2019) — which incorporates a DNAm-based surrogate for smoking pack-years and predicts time-to-death with Cox P = 2×10⁻⁷⁵ across large cohorts — illustrates how tightly smoking biology is woven into mortality risk. A meta-analysis of 84 telomere studies (Astuti et al. 2017) confirmed shorter leukocyte telomere length in current smokers versus never-smokers, consistent with increased oxidative DNA damage. Evidence is predominantly observational; causal inference rests on biological plausibility and dose-response patterns, while randomised cessation trials measuring epigenetic endpoints remain limited in size.

Photoaging is the cumulative dermatological damage caused by chronic exposure to solar ultraviolet (UV) radiation, distinct from intrinsic chronoaging. UVA (320–400 nm) penetrates the dermis, generates reactive oxygen species, and induces matrix metalloproteinases (notably MMP-1, MMP-3, MMP-9) that degrade collagen and elastin, producing wrinkles, laxity, and solar elastosis. UVB (280–320 nm) is absorbed in the epidermis, forming cyclobutane pyrimidine dimers and 6-4 photoproducts in DNA; unrepaired lesions drive non-melanoma skin cancer. A single 2 MED UVB exposure suppresses procollagen synthesis for ~24 h. Beyond UV, the skin-aging exposome also includes infrared-A, visible light, particulate air pollution and tobacco smoke. Daily broad-spectrum photoprotection (SPF 30+, UVA-PF ≥ 10) is the only intervention with consistent evidence for slowing measurable photoaging.