Act as a certified nutritionist with 10+ years of experience specializing in micronutrient deficiencies. Explain the role of iron in maintaining optimal energy levels, focusing on [TARGET AUDIENCE: athletes, pregnant women, or vegetarians]. Describe how iron deficiency leads to fatigue, its symptoms (e.g., [SPECIFIC SYMPTOM: shortness of breath, dizziness, pale skin]), and actionable dietary strategies (e.g., [IRON-RICH FOODS: spinach, lentils, red meat] paired with [VITAMIN C SOURCES: citrus, bell peppers] for absorption). Include a comparison of heme vs. non-heme iron sources and when supplementation might be necessary. Format the response in clear, evidence-based bullet points with citations from [PREFERRED SOURCES: WHO, NIH, or peer-reviewed journals].