Optimal Timing for Taking Supplements and Probiotics According to Science

Eating a balanced diet is the best way to get our vitamins and minerals, with food being the go-to source instead of supplements. Most healthy adults in the UK don't need many supplements, with vitamin D being the main one to consider during the autumn and winter months since there's not enough sunlight in Britain for our bodies to make enough naturally. Some of us might need extra help, like folic acid during pregnancy, iron if we have a deficiency, and vitamin B12 for vegans or those with limited diets. Other than that, a varied diet full of veggies, fruits, whole grains, protein, and healthy fats usually does the trick.

Through paying attention to when and how we consume our supplements, we can though optimise their benefits and ensure we are supporting our health in the most effective way possible.

If we do want to boost effectiveness, Vitamin D is a prime example where timing and what we eat can make a difference in absorption. Since it's a fat-soluble vitamin, it absorbs better when we take it with some dietary fat. A large study by Mulligan and Licata, published in the Journal of Bone and Mineral Research in 2010, showed that those who took vitamin D supplements with their largest meal saw a significant improvement in their vitamin D blood levels compared to those who took the supplements on an empty stomach. Researchers found about a 50% increase in serum vitamin D levels when the supplements were taken with meals that included fat. This supports broader nutritional evidence suggesting that foods such as eggs, yoghurt, avocado, nuts and oily fish may improve vitamin D absorption. Some researchers have also suggested that taking vitamin D very late at night could theoretically interfere with melatonin production and sleep, although evidence remains inconclusive. For most of us, taking vitamin D with breakfast or lunch is considered practical, effective and easy to maintain consistently.

Iron supplementation is another area where timing matters biologically because many foods and drinks inhibit absorption. Tannins found in tea, coffee and red wine can significantly reduce iron uptake. The tannins are polyphenolic compounds that can bind to iron in the digestive tract, forming complexes that the body cannot absorb. This binding effect is particularly pronounced when tea is consumed during or immediately after meals, as the presence of food can exacerbate the inhibitory effects on iron uptake. Iron supplements are therefore often recommended first thing in the morning on an empty stomach.

Certain foods may also interfere with iron absorption, including compounds known as goitrogens. Goitrogens are naturally occurring substances found in foods such as raw cruciferous vegetables — including kale, cabbage, broccoli and cauliflower — as well as soy products and may also modestly affect iron absorption by binding minerals within the digestive tract. Phytates, which are found in legumes, whole grains and soybeans, can reduce the absorption of non-haem iron, the form of iron found in plant foods and many supplements. This does not mean we should avoid healthy vegetables or plant foods, which remain highly nutritious, but it does suggest that individuals with iron deficiency may benefit from separating iron supplements from large quantities of soy, bran or high-phytate foods. Cooking cruciferous vegetables also reduces much of their goitrogenic activity.

Beneficially though vitamin C rich foods can be paired with iron-rich foods to aid the absorption of this heavy metal. Naturally vitamin C-rich foods such as citrus fruits, kiwi or berries can all be considered as part of or immediately after an iron rich meal.

Iron supplements are therefore often recommended first thing in the morning with a small glass of orange juice or on an empty stomach. Importantly, if iron causes nausea or digestive discomfort, taking it with a small amount of food is generally preferable to missing doses altogether — another reminder that consistency matters more than perfect timing.

Vitamin B12 is something to keep an eye on, especially if we are vegan or mostly eat plant-based foods. This vitamin is crucial for making red blood cells, keeping our nervous system in check, and helping with DNA synthesis. But here's the catch: B12 is found mainly in animal products like meat, fish, eggs, and dairy. A study by Pawlak and team in 2013, published in Nutrients, pointed out that vegans are more likely to lack B12 unless they regularly eat fortified foods or take supplements. While it doesn't really matter what time of day we take B12, there is some evidence that having it in the morning may give a slight energy boost. Being water soluble we cannot store B12 in our bodies for long, so It is crucial to ensure a consistent intake over time, as a deficiency can lead to fatigue, anemia, and neurological issues.

Probiotics - those gut friendly microbes - remain one of the most debated supplements when it comes to timing. Some studies suggest probiotics survive best when taken with food or shortly before eating because food can buffer stomach acid and help bacteria survive the digestive process. A study by Tompkins, Mainville and Arcand published in Beneficial Microbes in 2011 found improved bacterial survival when probiotics were taken with meals containing some fat. However, other researchers have suggested bedtime supplementation may also offer advantages. The theory is that stomach acid production and digestive activity tend to slow during sleep, potentially creating a more favourable environment for beneficial bacteria to survive passage through the stomach and colonise the gut. Some probiotic manufacturers therefore recommend taking supplements just before bed, particularly on a relatively empty stomach.

In addition, whilst we are slumbering, this is when the gut is repairing and getting revitalised for the following day's activity and may benefit from some probiotics to help the process. While evidence remains mixed and strain-specific, most experts agree that the differences between morning and evening supplementation are relatively small compared with the importance of taking probiotics regularly over time.

Ultimately, supplements can play an important role in supporting health in specific situations, but they are not a substitute for good nutrition. If in doubt we should always be guided by a healthcare professional. The evidence suggests that timing can modestly improve absorption in some cases — such as taking vitamin D with fat or separating iron from tea and coffee — but the single most important factor is consistency. Experts state that a routine and taking them regularly over time is way more important than the exact time we take them. Basically, taking our supplements every day is the best advice though if we wish to achieve optimum nutrition and efficacy we can consider when we take them and with what food and drink.

Happy eating,

Nina Thomas

BSc (Hons), MSc, ANutr

Registered Associate Nutritionist & Food Scientist

Bridgford & Bingham Nutrition              

21 Brickyard Lane

East Bridgford

Nottingham

NG13 8NJ

Call: 07958 765337

​www.bridgfordbinghamnutrition.co.uk