In the News: L-Theanine Supports Healthy Sleep

Consuming L-theanine can support healthy sleep, a systematic review of clinical trials concluded.*

Researchers identified 11 randomized, controlled trials plus two single-arm trials that examined the effects of theanine as a standalone nutrient among a total of 550 participants aged 9–57 years. L-theanine doses ranged from 50 mg–900 mg per day. All but two trials evaluated doses between 200 mg and 450 mg. Trial durations ranged from one day to eight weeks.

Statistically significant beneficial outcomes or trends toward beneficial effects were associated with L-theanine in nine trials, with improvements in both objective sleep evaluations and participant-reported sleep measures.

Although total sleep time did not increase, sleep latency, efficiency, maintenance and satisfaction, and feelings of refreshment and recovery upon waking improved in theanine-treated participants. L-theanine was not associated with drowsiness.

Editor’s Note: "Based on the current evidence, supplementation with 200-450 mg/day of L-theanine appears to be a safe and effective way to support healthy sleep in adults," the authors stated. 

* Nutr Neurosci. 2025 Nov 1:1-15.

Fish Oil Consumption Reduces Early Markers of Type 2 Diabetes Risk

A recent double-blind, randomized, controlled trial found that fish oil supplementation over 12 weeks significantly improved early biomarkers associated with type 2 diabetes risk.*

In the study, around 200 people were randomly assigned to one of four groups: a control group or one of three fish oil groups receiving daily doses of 310 mg, 620 mg, or 1,240 mg of EPA and DHA (key omega-3 fatty acids).

After 12 weeks, all fish oil groups showed increased serum levels of EPA and DHA, with the highest dose yielding the greatest rise.

Compared to the control group, those receiving fish oil experienced significant reductions in fasting insulin levels and HOMA-IR index (a marker of insulin resistance)—two important indicators of diabetes risk and status.

Editor’s Note: Fasting blood glucose exhibited a downward trend, with all fish oil groups showing a significant reduction compared with the beginning of the study.

* Food Funct. 2025 May 30:12:1598588.

Vitamin D3 Benefits Women with Polycystic Ovary Syndrome

A randomized, controlled clinical trial suggests that vitamin D3 supplementation may offer several important benefits for women with polycystic ovary syndrome (PCOS).*

Study participants received either vitamin D3 (30,000 IU/week) or a placebo for 12 weeks. This was followed by an additional 12 weeks in which every woman received the same vitamin D treatment. Women with inadequate dietary calcium intake also received supplemental calcium.

Vitamin D3 treatment led to improvements in ovarian morphology (the size, shape, and structure of the ovaries) and more regular menstrual cycles in over half of the participants. Additionally, the ovulation rate increased significantly.

Editor’s Note: Vitamin D deficiency is common in women with PCOS, the authors stated. They concluded that, "Our results suggest that vitamin D3 treatment could function as either a standalone or an adjunctive therapy in the management of PCOS".

* Nutrients. 2025 Apr 2;17(7):1246.

Multivitamin Use May Lower Risk of Prostate Cancer Recurrence

An association was found between the use of multivitamins and a reduction in the risk of prostate cancer recurrence, according to a recently published study.*

Participants included 1,396 men enrolled in the Cancer of the Prostate Strategic Urologic Research Endeavor (CaPSURE) between 1999 and 2018. The men received treatment with radiation or removal of the prostate for nonmetastatic prostate cancer. Responses to health questionnaires completed after diagnosis provided information concerning the use of multivitamins.

Prostate cancer recurred in 119 men during a median follow-up of 4.7 years. Men who reported supplementing with multivitamins had a 49% lower risk of disease recurrence compared with men who had never used multivitamins.

Among multivitamin users whose prostate cancer was of medium grade or higher, the risk of recurrence was 73% lower than among those who never used them.

Editor’s Note: The authors stated that oxidative stress is a risk factor for the onset and progression of prostate cancer. This suggests that multivitamins’ antioxidant properties may be responsible for the protective effect observed in this study.

* Eur Urol Oncol. 2025 May 6: S2588-9311(25)00110-5.