In screening for breast cancer (BC), mammographic breast density (MBD) is a powerful risk factor that increases breast carcinogenesis and synergistically reduces the sensitivity of mammography. It also reduces specificity of lesion identification, leading to recalls, additional testing, and delayed and later-stage diagnoses, which result in increased health care costs. These findings provide the foundation for dense breast notification laws and lead to the increase in patient and provider interest in MBD. However, unlike other risk factors for BC, MBD is dynamic through a woman’s lifetime and is modifiable. Although MBD is known to change as a result of factors such as reproductive history and hormonal status, few conclusions have been reached for lifestyle factors such as alcohol, diet, physical activity, smoking, body mass index (BMI), and some commonly used medications. Our review examines the emerging evidence for the association of modifiable factors on MBD and the influence of MBD on BC risk. There are clear associations between alcohol use and menopausal hormone therapy and increased MBD. Physical activity and the Mediterranean diet lower the risk of BC without significant effect on MBD. Although high BMI and smoking are known risk factors for BC, they have been found to decrease MBD. The influence of several other factors, including caffeine intake, nonhormonal medications, and vitamins, on MBD is unclear. We recommend counseling patients on these modifiable risk factors and using this knowledge to help with informed decision making for tailored BC prevention strategies.

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B reast cancer (bc) is the most commonly diagnosed cancer in women in the United States and the second most common cause of female cancer deaths. 1 As such, many female patients present to primary care physicians for further guidance regarding their concerns and risks of developing BC. Risk assessment involves a signifi cant amount of time to complete with many available risk calculation models, all of which have varied limitations. [2][3][4][5] However, a personalized risk assessment for BC should be performed, to some degree, in all female patients using a combination of risk calculators and obtaining a complete medical history of BC risk factors. Approaching patients systematically; gathering basic information such as age, body mass index (BMI), family BC history, reproductive risk factors; and gathering specifi c risk factors such as known genetic mutations, prior chest radiation, or history of atypical hyperplasia or lobular carcinoma in situ (LCIS) can help determine which patients need more formal and in-depth evaluation. This can be undertaken by the primary care clinician or a high-risk BC specialist and lead to shared decision making regarding screening and risk-reduction strategies. Some patients need not undergo extensive BC risk calculation if already considered high risk.It is prudent to consider the patient's personal values, individual risk factors, as well as differences in BC screening recommendations by societies and organizations (Ameri-