Caffeine and coffee can have different effects on glucose metabolism. Caffeine by itself may acutely reduce insulin sensitivity and temporarily raise glucose in some people, especially around meals, stress, poor sleep, or morning cortisol. However, habitual unsweetened coffee consumption is consistently associated with lower risk of impaired glucose tolerance and type 2 diabetes, including in studies of both caffeinated and decaffeinated coffee. For most people with prediabetes, moderate coffee can fit into a healthy lifestyle, but it should not worsen sleep, anxiety, reflux, blood pressure, or glucose control — and it should not be turned into a sugary drink.

PDE5 inhibitors such as sildenafil, tadalafil, and vardenafil are established medications used for erectile dysfunction and certain vascular conditions. Emerging observational and preclinical research suggests they may be associated with lower colorectal cancer risk and possibly improved colorectal cancer outcomes, but this evidence remains hypothesis-generating rather than practice-changing. No randomized trial has proven that these medications prevent or treat cancer, and concerns such as confounding, healthy-user bias, and a possible melanoma signal mean they should not be used for cancer prevention outside of appropriate medical indications or clinical trials.

Vitamin C is essential for collagen production, immune function, antioxidant defense, wound healing, and blood vessel health. While supplementation may modestly shorten common cold duration and slightly lower blood pressure, it is not proven to extend lifespan or replace the benefits of a plant-rich diet. For most healthy adults, vitamin C is best obtained from whole foods like citrus, berries, kiwi, bell peppers, broccoli, and leafy greens, which provide fiber, polyphenols, potassium, and other protective compounds beyond vitamin C alone.