Manganese is essential for the normal physiological functioning of humans, animals and plants. Exposure to low levels of manganese through diet is considered nutritionally essential in humans. Naturally ubiquitous in the environment, manganese can be found in rocks, soils, rivers, underground waters and foods such as nuts, legumes, seeds, tea, whole grains, and leafy green vegetables to name but a few. Considered as an essential nutrient, the body requires it to function properly - break down fats, carbohydrates, proteins and for bone strengthening as part of several enzymes, hence people use it in medicines included with chondroitin sulfate and glucosamine hydrochloride (multi-ingredient products) to combat osteoarthritis.
Manganese deficiency is not common in humans. However, lack of manganese has been found to cause improper formation of bone and cartilage. In soils with reduced manganese content usually due to poor drainage, crops sown on such soils suffer from yellowing of leaves, brown spots and severely affected leaves wither.
Manganese in excess can cause health effects in humans and animals but excess conditions in plants/crops are rare.