As the days grow longer and there’s more natural light streaming through our windows, you might start wondering if there’s any point taking vitamin D supplements in spring and summer. Sure, a good dietary or supplemental source of this nutrient is deemed essential in the long winter months, but doesn’t your body make enough vitamin D itself when you get a little sun?

The short answer to that question is, not necessarily. The longer answer is that it’s not always best to rely on sun exposure for vitamin D synthesis. Why? Because the damaging effects of the sun’s ultraviolet radiation could quickly counteract the benefits of topping up your vitamin D, especially for younger children.

Also, there’s a complex chain of reactions that allow your body to create active vitamin D. This relies on adequate levels of cholesterol produced by the liver, as well as other nutrients. Without these, your body may struggle to create vitamin D even when the sun is blazing in high summer!

Vitamin D synthesis in spring and summer

For your body to be able to make its own vitamin D, your skin needs to be exposed to sunlight of a certain strength for a sufficient amount of time. In the UK, from around October to April, the sun isn’t strong enough for the reaction required in the skin to form vitamin D, so a supplemental source is essential to maintain good health.

From early April to the end of September, however, the sun can be our main source of vitamin D, but that doesn’t mean it’s always the healthiest source. For most people with fair skin, just fifteen minutes or so in strong sunlight between 11 a.m. and 3 p.m. can enable sufficient vitamin D synthesis. Any longer, however, and the risk of burning and skin cancer quickly increases thanks to damaging ultraviolet radiation.

Because of this risk, it’s smart to cover up with sun-proof clothing, sunscreen, and a wide brimmed hat, and to stick to the shade where possible. But, of course, all of these measures reduce your ability to synthesise vitamin D.

So, if you’re able to put proper limits on how much time your skin is exposed to the sun each day, great! For most of us, though, this is difficult to manage, with exposures quickly adding up. The safest path forward could be, then, to protect skin against the sun whenever we’re out and about and keep taking our vitamin D all year round.

Other benefits of year-round vitamin D supplementation

In addition to helping us stay sun-safe, taking a vitamin D supplement all year round can help us overcome any blockages in the vitamin D metabolic pipeline caused by a lack of other nutrients. For instance, to fully activate vitamin D in the body, we need a sufficient amount of magnesium.

A year-round vitamin D supplement, or a multinutrient supplement that contains vitamin D, can also help ensure that seniors and others who might not get regular outdoor time don’t lack for this nutrient.

The NHS recommends daily vitamin D supplements for the following groups:

• All babies from birth to 1 year old (whether breastfed or formula-fed) 
• All children aged 1 to 4 years old   
• Anyone who doesn’t get much sun exposure (such as anyone frail or housebound, in an institution such as a care home or prison, or where a person covers their skin when outdoors).

They also recommend considering a daily vitamin D supplement containing 10 micrograms (μg) of vitamin D for everyone over the age of 5 years.

After all, vitamin D deficiency has serious consequences, including a far greater risk of osteoporosis and bone fractures, falls, muscle weakness, and compromised immune function.[i]^,[ii]  Vitamin D has also been linked to benefits for brain function and mood.[iii]

Supplementing your diet with vitamin D is a convenient and effective way to ensure a good level of this essential nutrient whether it’s sunny outside or not. And if you’re currently stuck inside, it’s definitely a good idea to keep taking your vitamin D, which will help keep your immune system strong to better defend against viruses, bacteria, and other pathogens.[iv]

[i] Bikle DD. Vitamin D metabolism, mechanism of action, and clinical applications. Chem Biol. 2014; 21(3):319-29.

[ii] Holick M, Siris E, Binkley N, et al. Prevalence of Vitamin D inadequacy among postmenopausal North American women receiving osteoporosis therapy. J Clin Endocrinol Metab. 2005; 90(6):3215-24.

[iii] Spedding, S. Vitamin D and depression: A systematic review and meta-analysis comparing studies with and without biological flaws. Nutrients. 2014; 6(4):1501-18.

[iv] Prietl B, Treiber G, Pieber TR, et al. Vitamin D and immune function. Nutrients. 2013; 5(7):2502-21.