Micronutrients and Hydration
Micronutrients and Hydration tests vitamin and mineral functions, deficiency and excess risks, bioavailability, supplement interpretation, and fluid and electrolyte balance. Expect unit conversions, food-source reasoning, and practical hydration calculations.
Core rules
- Fat-soluble vitamins A, D, E, and K require bile and fat for absorption and can accumulate; water-soluble B vitamins and vitamin C are generally excreted more readily, though toxicity is still possible with large supplements.
- Bioavailability varies: heme iron is better absorbed than nonheme iron; vitamin C enhances nonheme iron absorption, while phytates, tannins, and calcium inhibit it. Calcium absorption is supported by adequate vitamin D status.
- Vitamin D is expressed in both micrograms and international units: 1 mcg = 40 IU. Common adult reference intake is 15 mcg (600 IU) daily, rising to 20 mcg (800 IU) in older adults in some frameworks.
- Hydration includes drinking water and water from food and other beverages. Needs rise with heat, exercise, fever, vomiting, diarrhea, pregnancy, and lactation.
Worked example
A supplement label states 800 IU vitamin D. Divide by 40: 800 ÷ 40 = 20 mcg. If a client also takes a multivitamin containing 10 mcg, total supplemental vitamin D is 30 mcg (1,200 IU). Compare this with the UL of 100 mcg/day (4,000 IU) for adults, while remembering that sun exposure and food also contribute.
Traps
Do not mix up IU and mcg. Do not assume more water is always better; excessive intake without electrolyte replacement can cause hyponatremia. Do not recommend high-dose fat-soluble vitamins casually. Do not ignore inhibitors when judging iron or calcium adequacy.