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Breast cancer (BC) has surpassed lung cancer as the most commonly diagnosed cancer among women in the US, as well as globally. A number of factors evidently contribute to the risk of developing BC, including age, physical activity, overweight/obesity, alcohol consumption, etc. It is of particular importance to study the role of body fatness and its potential influence on the risk of developing BC, as the number of individuals with obesity has increased with an alarming rate worldwide in recent decades. Epigenetics alterations are reversible, and do not alter the DNA sequence; however, they can affect gene expression via modifiable factors, including lifestyle and environmental factors. The present review article, in addition to providing overall reviews of obesity and BC in association with public health, concentrated on the epigenetic phenomena, with a focus on the well-studied DNA methylation, and its role in the association between obesity and BC. The present review aimed to provide insight into the understanding of the paradoxical effects of obesity on pre-vs. post-menopausal BC (pre-BC vs. post-BC), and describe the mechanisms through which folate metabolism/DNA methylation may be responsible for the protective effects of obesity on pre-BC. The literature presented in the present review article indicates that the epigenetic alterations represent a mediator in the association between obesity and BC; however, the mechanisms through which obesity differentially affects pre-vs. post-BC remain unclear. Further studies using animal models and the analyses of human tissue biopsies are thus required to delineate the paradoxical effects of obesity on BC. Contents1. Obesity and breast cancer 2. Epigenetic alterations in breast cancer 3. Obesity and DNA methylation 4. Obesity, DNA methylation and breast cancer 5. Folate metabolism in obesity and breast cancer 6. Conclusions and future perspectives Obesity and breast cancerPrevalence of breast cancer (BC). BC has surpassed lung cancer as the most commonly diagnosed type of cancer among women, with ~2.26 million new cases and ~685,000 deaths recorded globally in 2020. These numbers represent 24.5% of all new cancer cases and 15.5% of cancer-attributed mortality in women, respectively (1). In the US, the new cases of BC have also markedly increased, reaching top levels among all new cancer cases among women, with ~282,000 cases estimated in 2021 (30%); BC also represents the 2nd leading cause of cancer-related mortality, with 43,600 deaths (15%), coming only second following lung cancer (2).The BC incidence rates have consistently increased during the decades between 1970-2000 in a number of industrialized countries, likely reflecting changes in lifestyle associated with civilization and increased detection via mammographic screening. In the 2000s, the incidence rates had reached a

Scope The previous study shows that obesity‐promoted inflammation is responsible for the activation of the intestinal tumorigenic Wnt‐signaling. The present study aims to test a dietary strategy, dietary supplementation with a high dose of vitamin D (VD) or its combination with sulforaphane (SFN) to inhibit intestinal inflammation and obesity‐associated tumorigenesis. Methods and results Apc1638N mice are randomly divided into four groups: LF, a low‐fat diet (10 kcal% fat) with 200 IU VD; HF, a high‐fat diet (60 kcal% fat) with 200 IU VD; HFD, a high‐fat diet with 5000 IU VD; and HFDS, a high‐fat diet plus 5000 IU VD and 0.23 g SFN per ≈4000 kcal. VD administration decreased tumor incidence and size, and the co‐administration with SFN (HFDS) magnified the effects. Inflammation and Wnt‐signaling are suppressed by VD. The addition of SFN decreased the activity of histone deacetylase (HDAC) and increased autophagy. Conclusion The administration of VD, at 5000 IU level, exerts an anti‐inflammatory property and leads to suppressed intestinal Wnt‐signaling and tumorigenesis in obese mice. The molecular function of SFN on a high dose of VD supplementation, although displayed on the inhibition of HDAC and the activation of autophagy, needs further investigation.

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