Signs of a nutrient deficiency in adults can manifest in various ways, depending on the type of nutrient lacking. Common symptoms include persistent fatigue, weakness, and poor concentration, which might indicate a deficiency in iron or vitamin B12. Skin and hair changes, such as dryness or excessive hair loss, could suggest insufficient essential fatty acids or vitamins A and E. Frequent infections may signal low levels of zinc or vitamin C, while bone pain or fractures might indicate deficiencies in vitamin D or calcium. Regular health screenings and blood tests can help identify these issues early.