Signs of vitamin deficiencies relevant to athletes include fatigue, muscle weakness, and decreased immune function. For instance, a lack of vitamin D may lead to weakened bones, while low levels of iron can cause anemia, impairing athletic performance. Deficiencies in vitamins B12 and C can affect energy levels and recovery rates. Athletes should monitor their dietary intake and consider supplementation when necessary to ensure they meet their nutritional needs, as proper nutrition plays a vital role in performance and overall well-being.