Melatonin is a molecule synthesized in the brain by the pineal gland and in the gastrointestinal tract. Melatonin is also synthesized in other organisms including plants.
Melatonin is believed to be responsible for the synchrony of circadian rhythm, modulating sleep patterns with day and night.
Melatonin is an antioxidant and protects tissues from oxidative damage by free radical elements. Further more, melatonin induces synthesis of endigenous antioxidants such as superoxide dismtase (SOD).
Several researches indicate that melatonin protects the gastrointestinal tract from irritation, reduces stress-induced lesion formation and heals ulcer.
Below are lists containing natural plant sources of melatonin. Melatonin content is in nanogram (ng) per gram of plant sample.
Table 1: Melatonin sources ( Rieter and Tan, 2002).
| Melatonin source | Melatonin content (ng/g) |
| Huang-qin | 7,110 |
| St. John’s wort, flower | 4,390 |
| Fever few, green leaf | 2,450 |
| Fever few, gold leaf | 1,920 |
| St. John’s wort, leaf | 1,750 |
| White mustard seed | 189 |
| Black mustard seed | 129 |
| Wolf berry seed | 103 |
| Fenugreek seed | 43 |
| Sunflower seed | 29 |
| Fennel seed | 28 |
| Alfalfa seed | 16 |
| Green cardamom seed | 15 |
| Tart cherry fruit (Montmorency) | 15 |
| Flax seed | 12 |
| Anise seed | 7 |
| Coriander seed | 7 |
| Celery seed | 7 |
| Poppy seed | 6 |
| Milk thistle seed | 2 |
| Tart cherry fruit (Balaton) | 2 |