Theaflavin, a polyphenolic compound found in black tea, has been investigated for its potential role in supporting metabolic health, including components of Metabolic Syndrome (MetS) such as obesity, dyslipidemia, insulin resistance, and hypertension. Several preclinical studies, primarily in animal models and in vitro, have demonstrated that theaflavins can exert beneficial effects on lipid metabolism, reduce blood glucose levels, decrease inflammation, and improve endothelial function. For example, research has shown that theaflavin supplementation may inhibit adipogenesis, modulate enzymes involved in fat metabolism, and reduce oxidative stress, which are all relevant to MetS pathophysiology.

Some small human clinical trials have suggested that black tea or theaflavin-rich extracts can modestly improve cholesterol profiles and glycemic control, but the sample sizes and durations are limited. A few meta-analyses of randomized controlled trials (RCTs) on tea polyphenols (including theaflavins) support modest improvements in LDL cholesterol and fasting glucose, but the effects are generally small and not always clinically significant. There is not yet robust evidence from large-scale, long-term human trials to conclusively confirm the efficacy of theaflavin for treating or preventing Metabolic Syndrome as a whole.

In summary, while there is scientific interest and some supportive data, the evidence base remains preliminary and limited mainly to preclinical studies and small human trials. Theaflavin is not traditionally used for Metabolic Syndrome, and its use for this purpose is primarily experimental at this time.