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You might know vitamin D as a nutrient solely responsible for efficient calcium absorption and therefore skeletal health, but Dr Sarah Brewer, Healthspan Medical Director, says this super vitamin helps to 'maintain a healthy immune system, may help to control blood sugar1 levels and could have an impact on your mood, too.'
But how can we ensure we get enough vitamin D on a daily basis? And if we're hoping to source our vitamin D through diet, is it even possible to reach the recommended intake this way? If so, how much do we need to consume? People that live in UK can't get vitamin D from the sun due to the UVB rays not being strong enough or variable throughout the year, so is diet a reliable method of ensuring we don't become deficient in this essential vitamin? We've teamed up with Dr Sarah Brewer to answer these questions.
The optimal level of vitamin D for one person is much higher than we once thought. When vitamin D was all about calcium absorption, the recommended intake was just 5mcg per day. Now the National Institute for Health and Care Excellence (NICE) recommends that all adults in the UK take a daily supplement containing 400IU (10mcg) of vitamin D throughout the year.
Research now suggests that many people need higher amounts to maintain good vitamin D status – especially in later life.2 Many experts are calling for everyone to supplement at a higher level all year round. The majority of adults need between 25mcg (1,000 IU) to 50mcg (2,000 IU) of vitamin D per day for optimum health, especially if they're already deficient or have a higher risk of deficiency.3
One thing we do know is Brits – on average – are lacking in vitamin D. The latest National Diet and Nutrition Survey (NDNS) results show that 17% of adults have low levels of vitamin D all year round.
Unfortunately, the absorption of vitamin D varies significantly per person based on factors such as skin colour and weight. For example, those with darker skin absorb less vitamin D from the sun, and those who have a larger fat percentage tend to have a higher risk of vitamin D deficiency, due to them absorbing nutrient supplements less effectively.4 Using sunscreen with a high SPF also reduces vitamin D production in the skin by screening out UV rays.
During autumn and winter in the UK your skin cannot react with sunlight to produce vitamin D. Put simply, the UVB rays emitted by the sun at this time - October through to early April- are not strong enough, meaning diet is the only source of this nutrient.
Even during the summer months, the amount of vitamin D we make from the sunshine on our bare skin is highly variable. Some of the factors that affect how much vitamin D we make in our skin include:
Not only this, many of us simply don't get enough sun exposure. We spend too much time indoors, or we cover up with sunscreen (something we must do to protect our skin) when we're outside, which inhibits vitamin D synthesis.
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Sadly, there are few reliable dietary sources of vitamin D. This is especially the case for vegetarians and vegans as vitamin D is split into two different types - vitamin D2 and vitamin D3. The latter (vitamin D3) comes from animals and is twice as effective at raising vitamin D levels in the body compared to its plant-based vitamin D2 counterpart.5
Many vegan milks, cereals, and juices are fortified with vitamin D2 which is less easily absorbed by the body. Most products contain very low amounts of the nutrient, too - typically 0.75 mcg (30 IU) per 100ml.
The food group highest in vitamin D3 is oily fish, which includes salmon, sardines, and mackerel. To give context, a small fillet of salmon (about 80g) provides around 10 mcg (400 IU) of vitamin D3, although factors such as the species of salmon, whether it's wild or farmed and the season during which the fish was caught may affect this estimation. Sardines and mackerel are also good sources of vitamin D3, with 80g of mackerel providing roughly 10 mcg (400 IU) of vitamin D and a small tin of sardines (120g) roughly 6 mcg (240 IU).6
While oily fish is a good source of vitamin D3, most of us are unlikely to eat it every day. Additionally, the most you're likely to get from one portion is 10 mcg (400 IU) - perhaps less. Given that the average Brit needs at least 25 mcg (1000 IU) of vitamin D per day, you'd have to eat several fillets of wild salmon, or five whole tins of sardines daily to reach this target.
Another good source of vitamin D3 is beef liver, with 80g providing up to 1 mcg (40 IU). While this allows you to top up your intake, it would be unrealistic and unhealthy to eat the equivalent to 25 mcg (1000 IU). Likewise, with egg yolks, which provide about1 mcg (40 IU) per egg. If you wanted to achieve a daily intake of 25 mcg (1000 IU) from eggs alone, you'd need to eat a whopping 25 eggs per day.6
It's easy to see why diet provides such a low proportion of our daily vitamin D requirements. There simply aren't enough vitamin D-rich foods that can feasibly be incorporated into our diet. Diet should always come first, so while it cannot provide enough vitamin D to stop deficiency and support optimal levels, it's important not to discount food sources of vitamin D as an important top-up. Every little helps, after all.
The reality is a vit D supplementation is the most effective and least invasive solution to maintaining healthy levels of vitamin D. Taking just one vitamin D supplement daily, all year round, helps to ensure that you're getting enough every single day. No need for infeasible diets or continuous sun exposure.
This doesn't mean we should discount the sunshine or our diet as helpful ways to keep our vitamin D levels topped up. Rather, we should be looking to use supplements alongside the right food and sensible sun exposure to ensure we're not deficient in what's proven to be an absolutely essential nutrient.
Nothing beats a healthy, balanced diet to provide all the nutrients we need. But when this isn't possible, supplements can help. This article isn't intended to replace medical advice. Please consult your healthcare professional before trying supplements or herbal medicines.
1Lee, CJ. Iyer, G. Liu, Y. Kalyani, RR. Bamba, N. Ligon, CB. Varma, S. Mathioudakis N., The effect of vitamin D supplementation on glucose metabolism in type 2 diabetes mellitus: A systematic review and meta-analysis of intervention studies.(2017). J Diabetes Complications 31(7).
2Heaney. R, (2006), Barriers to Optimizing Vitamin D3 Intake for the Elderly The Journal of Nutrition, Volume 136, Issue 4.
3Summary of Key Findings from the NDNS Report of Years 7 and 8 (combined), (2018), British Nutrition Foundation
4 Raed. A, Bhagatwala. J, Haidong. Z, Pollock. NK, Parikh. SJ, Huang. S, Havens. R, Kotak. I, Guo. D, Dong. Y (2017) Dose responses of vitamin D3 supplementation on arterial stiffness in overweight African Americans with vitamin D deficiency: A placebo controlled randomized trial, PLOS one,
5Bischoff-Ferrari HA, (2014), Optimal serum 25-hydroxyvitamin D levels for multiple health outcomes, Adv Exp Med Biol. 810:500-25.
6Dawson-Hughes. B, (2004), Racial/ethnic considerations in making recommendations for vitamin D for adult and elderly men and women, Am J Clin Nutri, 80.
7Pereria-Santos. M, Costa. PR, Assis. AM, Santos. CA, Santos. DB, (2015), Obesity and vitamin D deficiency: a systematic review and meta-analysis, Obes Rev 16 (4): 341-9.
8Holick. MF, Binkley. NC, Bischoff-Ferrari. HA, Gordon. CM, Hanley. DA, Heaney. RP, Murad. H, Weaver. CM, (2011), Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society
9Clinical Practice Guideline. J Clin Endocrinol Metab 96:1911-30.
10L. Tripkovic, H. Lambert, K. Hart, C. P. Smith, G. Bucca, S. Penson, G. Chope, E. Hypponen, J. Berry, R. Vieth, S. Lanham-New, (2012), Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. American Journal of Clinical Nutrition 95 (6): 1357.
11 Schmid. A, Walther. B, (2013), Natural Vitamin D content in animal products, Adv Nutr., 1;4(4):453-62.
12Heaney. RP, Armas. LA, French. C, (2013), All-source basal vitamin D inputs are greater than previously thought and cutaneous inputs are smaller, Journal Nutrition, 143 (5): 571-5.