To combat afternoon fatigue, especially for a 39-year-old in-shape male, several supplements have shown effectiveness based on research:

1. Vitamin D: Low levels of vitamin D have been associated with fatigue. Supplementation with vitamin D has shown improvements in fatigue, especially in individuals with initially low levels¹.
2. Iron: Iron supplementation can reduce fatigue, even in non-anemic athletes. Studies have shown that low-dose iron can improve stress, mood states, and reduce fatigue².
3. Melatonin: Known primarily for its role in regulating sleep, melatonin can help improve sleep quality and reduce daytime fatigue. It's especially helpful for those experiencing poor sleep quality³.
4. Magnesium: This mineral helps with muscle relaxation and sleep regulation. It has been shown to improve overall sleep quality and efficiency⁴.
5. Panax Ginseng: G115® extract from Panax ginseng, combined with vitamins and minerals, has been shown to significantly reduce self-perceived fatigue and improve energy levels⁵.
6. Nicotinamide Mononucleotide (NMN): NMN has demonstrated effectiveness in improving sleep quality and reducing drowsiness when taken in the afternoon⁶.

If you need product recommendations for these supplements, please let me know!

Footnotes

1. Albina Nowak et al., Effect of vitamin D3 on self-perceived fatigue, PubMed Central ↩

2. Mahendra P. Kapoor et al., Influence of iron supplementation on fatigue, mood states and sweating profiles, PubMed Central ↩

3. Gorica Djokic et al., The Effects of Magnesium – Melatonin - Vit B Complex Supplementation in Treatment of Insomnia, PubMed Central ↩

4. Gorica Djokic et al., The Effects of Magnesium – Melatonin - Vit B Complex Supplementation in Treatment of Insomnia, PubMed Central ↩

5. Anne-Laure Tardy et al., Reduced Self-Perception of Fatigue after Intake of Panax ginseng Root Extract (G115®), PubMed Central ↩

6. Mijin Kim et al., Effect of 12-Week Intake of Nicotinamide Mononucleotide on Sleep Quality, Fatigue, and Physical Performance, PubMed Central ↩