{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,1]],"date-time":"2026-07-01T13:45:06Z","timestamp":1782913506047,"version":"3.54.5"},"reference-count":29,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2026,6,27]],"date-time":"2026-06-27T00:00:00Z","timestamp":1782518400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Toxics"],"abstract":"<jats:p>Background: Secondhand exposure to heated tobacco products (HTPs) is increasingly common, but its impact on human milk composition is unclear. We investigated whether secondhand exposure to HTP aerosols affects major human milk components and cotinine concentrations in lactating women. Methods: This observational study included 15 lactating women whose household members used HTPs (secondhand HTP exposure group) and 33 lactating women who did not live with any smokers (non-exposed group). Human milk was analyzed for macronutrients, total solids, energy, lactoferrin, secretory immunoglobulin A (sIgA), calcium, inorganic phosphorus, zinc, and cotinine. Cotinine was measured in all women in the secondhand HTP exposure group and in three women in the non-exposed group. Results: Background characteristics did not differ significantly between groups. No significant differences were observed in lipid, protein, total solids, energy, true protein, lactoferrin, calcium, inorganic phosphorus, or zinc. Carbohydrate concentration differed significantly between the non-exposed and secondhand HTP exposure groups (non-exposed vs. secondhand HTP exposure: 8.20 vs. 8.10 g\/dL, p = 0.032), although the absolute difference was small. sIgA tended to be higher in the secondhand HTP exposure group (non-exposed vs. secondhand HTP exposure: 1244 vs. 1706 \u03bcg\/mL, p = 0.072). Cotinine concentrations did not differ significantly between groups; qualitative cotinine tests were negative in all samples. Conclusions: Secondhand exposure to HTPs was not associated with clear differences in major human milk components or cotinine concentrations. However, the findings should be interpreted cautiously because of the small sample size and limited cotinine assessment. Larger studies with objective exposure assessment and infant follow-up are needed.<\/jats:p>","DOI":"10.3390\/toxics14070563","type":"journal-article","created":{"date-parts":[[2026,6,30]],"date-time":"2026-06-30T00:55:11Z","timestamp":1782780911000},"page":"563","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Effects of Secondhand Exposure to Heated Tobacco Products on Human Milk Composition"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0009-0003-5700-9364","authenticated-orcid":false,"given":"Masako","family":"Tateno","sequence":"first","affiliation":[{"name":"Department of Pediatrics, Showa Medical University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8666, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6983-8851","authenticated-orcid":false,"given":"Katsumi","family":"Mizuno","sequence":"additional","affiliation":[{"name":"Department of Pediatrics, Showa Medical University School of Medicine, 1-5-8 Hatanodai, Shinagawa-ku, Tokyo 142-8666, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Midori","family":"Date","sequence":"additional","affiliation":[{"name":"The Nippon Foundation Human Milk Bank, 17-10 Nihonbashi-koamicho, Chuo-ku, Tokyo 103-0016, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2690-3780","authenticated-orcid":false,"given":"Miori","family":"Tanaka","sequence":"additional","affiliation":[{"name":"The Nippon Foundation Human Milk Bank, 17-10 Nihonbashi-koamicho, Chuo-ku, Tokyo 103-0016, Japan"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,6,27]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"30","DOI":"10.1177\/003335490812300105","article-title":"Reducing levels of toxic chemicals in cigarette smoke: A new Healthy People 2010 objective","volume":"123","author":"Richter","year":"2008","journal-title":"Public Health Rep."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"734","DOI":"10.1542\/peds.2010-3041","article-title":"Secondhand smoke and adverse fetal outcomes in nonsmoking pregnant women: A meta-analysis","volume":"127","author":"Britton","year":"2011","journal-title":"Pediatrics"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"489","DOI":"10.2188\/jea.JE20210405","article-title":"Tobacco Exposure During Pregnancy and Infections in Infants up to 1 Year of Age: The Japan Environment and Children\u2019s Study","volume":"33","author":"Hashimoto","year":"2023","journal-title":"J. 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