High intakes of some vitamins and minerals are just as harmful to health as not getting enough. Nutritional researchers have therefore identified tolerable upper safe levels (USLs or ULs) for long-term intakes but, as with recommended daily amounts (RDAs), these differ between countries.
Most of the tolerable upper intake levels suggested for different age groups within the United States are maximum intakes from both food and supplements. It’s difficult to know how these combined intakes relate to your individual diet, however, as the amount you consume varies from day-to-day, and even from season to season.
The most useful indicator for upper safe levels of daily doses when taking vitamin and mineral supplements are those suggested for guidance purposes by the UK Expert Group on Vitamins and Minerals in 2003. Apart from vitamin A, chromium and copper, these values relate to how much of each micronutrient you can take on a daily basis, long-term, in the form of supplements. These values are in addition to the amounts obtained from food and drinking water (except where indicated). Slightly different tolerable upper intake levels have since been adopted in the EU for some micronutrients, although they were unable to determine a tolerable upper intake level for them all.
It’s not an exact science, and upper safe levels are revised regularly to take new findings into account. I strongly advise that you do not exceed the suggested safe upper levels unless you are advised to (on a short-term basis) by a healthcare professional to treat a proven deficiency. Higher doses can cause side effects (eg nausea, constipation, diarrhoea) and may be toxic in the long run (eg nerve damage). Excess iron is especially toxic – it’s therefore vital to keep your supplements out of the sight and reach of children.
Upper safe levels for vitamins
Vitamin A (retinol)
The upper safe level (USL) is 1500 mcg (5000 IU) from both food AND supplements in the UK. The EU and US suggest a tolerable upper level (from both food and supplements of 3000 mcg per day for men and women of child-bearing age (post-menopausal women may need more to reduce the risk of bone fractures).
If taking both a multivitamin and a cod liver oil (which also contains vitamin A), check the combined amount does not exceed the recommended daily amount of 800 mcg (2,664 IU) which leaves room for the amount likely to come from your food. Supplements designed for use in pregnancy do not normally contain any vitamin A as excess has been linked with developmental abnormalities.
Vitamin B1 (thiamin)
The UK USL is suggested as 100 mg for long-term use from supplements.
Vitamin B2 (riboflavin)
The USL is 40 mg from supplements.
Vitamin B3 (niacin)
The USL is 500 mg from supplements.
Vitamin B5 (pantothenic acid)
The USL is 200 mg from supplements.
Vitamin B6 (pyridoxine)
The USL suggested in the UK is 10 mg from supplements for long-term use. Levels between 10 mg and 200 mg may be used short-term, but intakes above 200 mg are not generally recommended except under medical supervision. The upper level suggested by the EU is 25 mg per day from supplements.
Vitamin B12 (cobalamin)
The USL is 2000 mcg from supplements.
Folic acid (folate)
The USL is suggested as 1000 mcg (1 mg) from supplements in both the UK and the EU. However it is widely accepted that an upper safe level of 400 mcg is preferable, as excess can mask the blood changes (enlarged red cells) that would allow diagnosis of pernicious anaemia which results from an inability to absorb vitamin B12.
The USL is 900 mcg from supplements.
Vitamin C (ascorbic acid)
The USL is 1000 mg (1 g) from supplements.
Vitamin D3 (cholecalciferol)
The USL is 100 mcg (4,000 IU) from supplements. This higher level was revised and updated within the EU in 2012.
Vitamin E (tocopherol)
The tolerable upper level is suggested as 300 mg (450 IU) from supplements in the EU. In the US, the upper safe level for adults is suggested as 1,500 IU/day for supplements providing natural vitamin E and 1,100 IU/day for supplements containing synthetic vitamin E.
The USL is 1000 mcg (1 g) from supplements.
Upper safe levels for minerals
The USL is 6mg from supplements.
The USL is 1,500 mg from supplements.
The USL is 10 mg from food AND supplements.
The USL is 10 mg from food AND supplements.
The USL is 500 mcg from supplements.
The USL is 17 mg from supplements (except under medical supervision to treat a confirmed iron deficiency). Note how similar this is to the UK/EU recommended daily amount (RDA) of 14 mg per day. It is actually below the Daily Value of 18 mg set in the US, where the combined Upper Intake Level per day is 45 mg from both food and supplements).
The USL is 400 mg per day from supplements in the EU, and 350 mg per day from supplements in the US. These values are in addition to intakes from food and drinking water and are similar to the recommended daily levels (EU RDA is 375 mg, US DV is 400 mg). This is because some people taking above 400 mg per day experience loose bowels. Because of this, a lower level of 250 mg per day from supplements was suggested as the tolerable upper intake level within the EU.
The USL is 4 mg from supplements.
The USL is 250 mg from supplements (which is significantly below the recommended daily amount that you need to obtain from food).
The USL is 3,700 mg from supplements.
The UK USL is 350 mcg from supplements. The EU derived a tolerable upper intake level that was lower, at 300 mcg per day from all sources, including food and supplements.
The USL is 25 mg from supplements.
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