Vitamins A, D, E and K dissolve in fat rather than water and are absorbed along with it. So a capsule swallowed with water on an empty stomach can be absorbed several times worse than the same capsule at lunch. The same goes for fish oil.
Vitamin D — with your most substantial meal
In a study by Dawson-Hughes and colleagues (2015), 50 older adults took the same dose of vitamin D3 with a fat-free breakfast or one with 30% of calories from fat. With the fatty breakfast, blood vitamin D was 32% higher, and the type of fat made no difference.
In a small study by Mulligan and Licata (2010), 17 patients whose vitamin D levels weren’t rising on treatment started taking the same dose with their largest meal — and within 2–3 months their levels rose on average from 30.5 to 47.2 ng/mL. There was no control group, but the result is consistent with the study above.
Vitamin E — even more clearly
Taken with a fat-free breakfast, 10% of vitamin E was absorbed; with 6% of calories from fat, 20%; with 21%, 33% (Bruno et al., 2006). And a 400 IU capsule taken with skimmed milk on an empty stomach produced 26 times less vitamin E in the blood than the same dose in fortified cereal (Leonard et al., 2004).
The form matters too
- Vitamin D3 or D2. In a meta-analysis, D3 raised blood vitamin D more than D2, especially in large single doses; with daily dosing the difference disappeared (Tripkovic et al., 2012).
- Natural or synthetic vitamin E. Natural vitamin E (“d-alpha-tocopherol” or RRR on the label) is about twice as available as synthetic (“dl-alpha-tocopherol”, all-rac) (Burton et al., 1998).
Fish oil: triglycerides or ethyl esters
Omega-3 capsules come in two forms. Ethyl esters (EE on the label) were absorbed only 20% as well as free fatty acids, and triglycerides (TG) 57–68% as well (Lawson, Hughes, 1988a). With a high-fat meal, ethyl ester absorption tripled to about 60%, and EPA from triglycerides rose from 69% to 90% (Lawson, Hughes, 1988b). So take omega-3 with a proper meal. How fish oil differs from flaxseed oil is covered in Flaxseed oil or fish.
What about vitamins A and K?
They’re fat-soluble too, so the same logic applies: take them with a meal that contains fat. With vitamin A, it’s also important not to overdo it: the safe upper limit for preformed vitamin A (retinol) from supplements is 3,000 µg, or 10,000 IU, a day.
In short
- Vitamins D, E, A, K and fish oil — with your most substantial meal that contains fat, not on an empty stomach.
- Vitamin D — preferably D3.
- Vitamin E — natural (d-alpha-tocopherol).
- Omega-3 — as triglycerides (TG); ethyl esters (EE) always with a fatty meal.
Fat-soluble vitamins build up in the body, so more isn’t better. The safe upper limit for vitamin D is 100 µg (4,000 IU) a day. How much you need in winter and who should take it is covered in Vitamin D in winter.
The CookCount diary has a Supplements section: you can enter vitamins D and A in IU, as on the label — the calculator converts them to micrograms, adds them to your food in the charts and history and warns you if a day goes over the safe upper limit. For minerals, see Magnesium, zinc, calcium and How to take iron.