Potassium supplements are limited to 100mg, however the RDA is 4.7g. From the foods I do eat (and will continue to do so), I get around 1.5g of potassium per day, which is way too little. However, is there something about potassium supplementation that is unsafe, or why are the supplements limited to 100mg exactly?
1) Multivitamin-mineral supplements in the US do not contain more than 99 mg of potassium per serving to avoid overdose.
Oral doses greater than 18 grams taken at one time in individuals not accustomed to high intakes may lead to severe hyperkalemia, even in those with normal kidney function.
In individuals with somewhat impaired kidney function (without them knowing it), the toxic dose can be considerably lower.
2) Foods that contain more than 500 mg potassium per serving: avocado, jackfruit, pomegranate, dates, kiwi, banana, potatoes, beet greens, tamarind, white beans, red salmon. Foods with 300-500 mg potassium: various fruits, legumes, fish and meats.
3) Strictly speaking, 4.7 g potassium/day is not Recommended Dietary Allowance (RDA), but Adequate Intake (AI), which is believed to cover the needs of all healthy adults (Institute of Medicine). The needs for nutrients in general increase with calorie needs. This means that AI 4.7 g potassium/day is what people with the highest needs (athletes, heavy physical workers) who spend more than 4 K Calories/day may need and not necessary what average adults who spend 2-2.5 K Calories/day need.
4) Additionally, according to National Academic Press:
Given the interrelatedness of sodium and potassium, the requirement for potassium may well depend on the level of dietary sodium...
So, if you decrease your sodium intake, your potassium needs will be likely lower.
5) If studies show that high intake of foods high in potassium is associated with health benefits, this does not automatically mean that potassium supplements are beneficial. This is because it is not actually known, is it potassium or are other nutrients (calcium, magnesium) in foods high in potassium, or their combination, which is actually beneficial.
High quality evidence shows that increased potassium intake reduces blood pressure in people with hypertension.
This systematic review found no statistically significant effect of potassium supplementation on blood pressure.