The purpose of the study is to understand the effect of the dietary supplement "Nicotinamide mononucleotide" on metabolic health in people.

This study is is looking at the effect of the dietary supplement "Nicotinamide mononucleotide" (NMN) on key cardiovascular and metabolic functions, specifically those that are important risk factors for diabetes and cardiovascular disease. Accordingly, the investigators will evaluate the effect of NMN on how well the hormone insulin works to control blood sugar. The investigators will also look at the effects of NMN on blood lipids; body fat and liver fat; and other blood, fat tissue and muscle tissue markers of cardiovascular (heart) and metabolic health. Data from studies conducted in rodents have shown that NMN supplementation has beneficial effects on cardiovascular and metabolic health, but this has not yet been studied in people.

Inclusion Criteria:

• Postmenopausal women 55-75 years old
• BMI 25.0-44.9 kg/m²
• Fasting plasma glucose concentration ≥100 mg/dl, OGTT 2 hour glucose ≥ 140 mg/dl, HbA1C ≥5.7%, or HOMA-IR ≥2.5

Exclusion Criteria:

• Diabetes
• Premenopausal or menopause <1 year
• Persons who have received hormone replacement therapy within the past 6 months
• Persons who take vitamin B supplementation and are not willing to discontinue supplementation for 3 weeks before and during the entire study period.
• Structured exercise: ≥75 min/wk of vigorous exercise (e.g., jogging, activity that causes heavy breathing and sweating) or ≥150 min/wk of low intensity physical activity (e.g., brisk walking).
• Unstable weight (>3% change during the last 2 months before entering the study)
• Significant organ system dysfunction or disease
• Present cancer or history of cancer that has been in remission for <5 years
• Polycystic ovary syndrome
• Major psychiatric illness
• Use of medications known to affect study outcome measures (e.g., steroid) or increase the risk of study procedures (e.g., anticoagulants) that cannot be temporarily discontinued for the study
• Metal implants
• Smokes cigarettes
• Persons who consume >14 units of alcohol per week
• Unable or unwilling to follow the study protocol or who, for any reason, is considered an inappropriate candidate for the study by the research team.