A Guardian article addresses the crucial, yet often misunderstood, topic of correct supplement usage and dosage limits. It underscores that despite their popularity, supplements are not inherently safe, and consuming excessive amounts of certain vitamins and minerals can lead to significant health problems. The article emphasizes that consumers should be aware of both Recommended Dietary Allowances (RDAs) and Tolerable Upper Intake Levels (ULs), which represent the maximum daily intake unlikely to cause adverse health effects. Key claims in the article, corroborated by multiple health authorities, include the necessity of consulting healthcare providers before starting new supplements due to potential interactions with medications or other supplements, and their impact on blood tests. The piece also highlights concerns over the limited government oversight in markets like the US, leading to potential inaccuracies in product labeling. Specific warnings are issued for several common supplements: excessive Vitamin C (above 2,000 mg/day for adults) can cause gastrointestinal upset; Vitamin D beyond 4,000 IU (100 mcg) daily for adults can lead to toxicity, including high calcium levels and kidney stones; high doses of Magnesium (over 350 mg/day from supplements for adults) can cause digestive issues, and very high doses can be fatal, especially for those with kidney problems; Iron overdose, even in relatively small amounts (10-20 mg/kg), can cause acute toxicity affecting organs and can be lethal in higher doses; and excessive Vitamin A (above 3,000 mcg RAE or 10,000 IU/day for adults) can result in liver abnormalities, bone issues, and birth defects. The article implicitly advises that nutrient intake should ideally come from a balanced diet, with supplements serving as a 'top-up' when necessary.