Vitamin D3 400iu vs 1000iu: Which Strength Should You Take?
By Nature's Best | Published: 2026-11-02
Category: Buying Guides
Compare low-dose vitamin D3 400iu with high-strength 1000iu, including vegan algae-based options, to choose the right daily supplement for your needs.
Quick answer
Choose 400iu if you already take a multivitamin or simply want a low-dose top-up; choose 1000iu if you get little sun exposure or prefer a single higher-strength capsule, including a vegan algae-based option.
Why the right strength depends on your full routine
Vitamin D supplements are not taken in isolation. Many multivitamins already supply 400iu of vitamin D3, so adding a separate 400iu tablet is a sensible top-up, while adding 1000iu on top of a multivitamin may push your total higher than you intended. Check the label of everything you take before deciding.
The UK Department of Health recommends that all adults consider taking a daily supplement containing 400iu (10μg) of vitamin D, particularly in winter. That baseline is why 400iu is often described as a low-dose or maintenance strength, while 1000iu is a higher-strength option for people who want more from a single capsule.
When a vegan formula changes the decision
Standard vitamin D3 tablets are not always suitable for plant-based diets because the D3 may come from lanolin (sheep's wool). If you follow a vegan diet, the source matters as much as the number on the label. Algae-derived D3 offers a plant-based route to the same nutrient, so a 1000iu vegan capsule can be the practical choice even if you only wanted a low dose, because strength and sourcing are separate questions.
Common questions about vitamin D3 strength
- Should I take 400iu or 1000iu?
- Take 400iu if you already take a multivitamin that contains vitamin D or you want the Department of Health-recommended winter baseline. Take 1000iu if you get very little sun exposure, want a higher strength in one capsule, or need a vegan formula. Add up the vitamin D in everything you take before choosing.
- Can I take 400iu and 1000iu together?
- There is no need to take both. If you take a 400iu multivitamin and want more, a single 1000iu capsule may be simpler than stacking a separate 400iu tablet on top. Check the total against your own needs. Avoid doubling up without checking your combined intake.
- Is 1000iu suitable for vegans?
- Only if the D3 is plant-sourced. The Vegan Vitamin D3 1000iu capsules are gelatine-free and algae-derived, so they fit a vegan diet. Standard D3 tablets may use lanolin, so always read the source on the label. Look for algae-derived D3, not just a vegan-friendly claim.
- Do I need a higher dose in winter?
- UK guidance recommends all adults consider 400iu daily in winter. If you get little sun exposure year-round, a higher strength such as 1000iu may be more appropriate, but individual needs vary. Winter is the minimum; year-round low sun exposure may justify more.
- Can I combine these with a multivitamin?
- Yes, but check the multivitamin's vitamin D content first. Most Nature's Best multivitamins already supply 400iu, so adding the 400iu tablet duplicates that amount. A 1000iu capsule may be a cleaner upgrade if you want more. Read the multivitamin label before adding any separate D3.
Product facts
- Vitamin D3 400iu: One-a-day Vitamin D3 400iu tablets provide the Department of Health-recommended amount all UK adults should consider taking in winter. This makes it a straightforward low-dose top-up if you do not already get 400iu from a multivitamin.
Vitamin D3 400iu - Vegan Vitamin D3 1000iu: Vegan Vitamin D3 1000iu capsules are gelatine-free and derived from algae, delivering 1000iu (25μg) per capsule. This suits plant-based diets and anyone who prefers a single higher-strength capsule rather than a low-dose tablet.
Vegan Vitamin D3 1000iu
