The “Big Dark”: Why Every Irish Household Needs Vitamin D3 From October to March

By October, Ireland’s days are getting shorter. You may leave for work in the dark, return after sunset, and spend far less time with enough sunlight on your skin to produce vitamin D.

The reason matters: because of Ireland’s northern latitude, winter sunlight does not provide enough UVB radiation for your skin to make sufficient vitamin D. From late autumn through early spring, dietary sources and supplementation therefore become more important.

For many people, taking vitamin D3 during the winter can help maintain an adequate intake, while some groups may need supplementation year-round. 

But who needs it, how much do you need, and which type of vitamin D3 supplement is right for you?

Why Ireland’s Winter Sun Isn’t Enough for Vitamin D

Your body can produce vitamin D when your skin is exposed to UVB rays from sunlight. During the brighter months, spending time outdoors can contribute to your vitamin D levels. But in Ireland, this becomes much more difficult during winter.

Because of Ireland’s northern latitude, the sun sits lower in the sky from late autumn through early spring. The UVB radiation reaching the ground is therefore not sufficient for your skin to produce enough vitamin D. So even being outdoors during daylight hours does not necessarily provide the sunlight exposure needed for vitamin D production.

Winter clothing also means less skin is exposed. Coats, jumpers, trousers, scarves and gloves keep you warm, but they naturally reduce the amount of skin that can receive sunlight.

Food can provide some vitamin D, particularly through sources such as oily fish and fortified foods. However, there are relatively few dietary sources, so it can be difficult to rely on food alone to meet vitamin D needs during the Irish winter.

This seasonal lack of sunlight is why vitamin D supplementation becomes particularly relevant in Ireland during the darker months.

Who Needs to Pay Particular Attention to Vitamin D?

Vitamin D needs can vary between people. In Ireland, age, skin type and how much time you spend outdoors can all affect whether you need seasonal or year-round supplementation. If you're concerned about vitamin D deficiency in Ireland, our guide explains the common causes, signs and ways to maintain healthy vitamin D levels.

Babies and Young Children

Babies and young children need vitamin D to support normal bone and teeth development, but their requirements differ from those of adults.

Babies have specific supplementation guidance depending on whether they are breastfed or how much infant formula they consume. Young children also have age-specific recommendations, so they should only be given a supplement formulated for their age and in the appropriate amount.

Adults Aged 65 and Over

The skin becomes less efficient at producing vitamin D as we age. Adults aged 65 and over are therefore advised to take vitamin D throughout the year rather than relying only on winter supplementation.

People With Darker Skin

Darker skin contains more melanin, which reduces the skin's ability to produce vitamin D from UVB exposure. People with darker skin aged 12–65 are advised to take vitamin D year-round rather than only during winter.

People With Limited Sun Exposure

Spending very little time outdoors or regularly covering most of your skin can reduce the amount of vitamin D your body produces from sunlight. People with limited sun exposure may need vitamin D supplementation throughout the year, depending on their circumstances. 

If you fall into one of these groups, the next question is how much vitamin D you actually need.

How Much Vitamin D3 Do You Need in Ireland?

The amount of vitamin D you need depends on your age, skin type and individual circumstances. Irish guidance also differs depending on whether you need supplementation during winter or throughout the year.

*For babies, supplementation depends on breastfeeding and infant-formula intake. HSE guidance recommends 5 µg (200 IU) of vitamin D3 daily for breastfed babies and babies taking less than 300 ml of infant formula per day. Babies taking more than 300 ml of formula generally do not need an additional vitamin D supplement.

Some people have specific year-round supplementation recommendations, including pregnant people and people with darker skin. 

For people who need seasonal supplementation, the recommended winter period in Ireland runs from Halloween to St Patrick’s Day.

More vitamin D isn't necessarily better

A higher-strength supplement isn't automatically more beneficial. Taking excessive amounts of vitamin D over time can cause calcium to build up in the body and may harm the kidneys and heart. Always follow the recommended dose on your chosen product.

It's also worth checking your other supplements. Multivitamins, cod liver oil and other products may already contain vitamin D, so taking several products together can unnecessarily increase your total intake.

If you've been diagnosed with vitamin D deficiency or advised to take a higher dose by your GP or healthcare professional, follow their individual recommendation rather than general supplementation guidance.

When Should You Take Vitamin D3 in Ireland?

For many healthy, fair-skinned people in Ireland, vitamin D supplementation is recommended from Halloween to St Patrick’s Day, when sunlight provides limited opportunity for the skin to produce vitamin D.

However, some people have different recommendations and may need supplementation throughout the year. These include people with darker skin, adults aged 65 and over, pregnant people and babies who require vitamin D supplementation.

If you're unsure whether seasonal or year-round supplementation is appropriate for you, speak with your pharmacist or GP.

Which Vitamin D3 Supplement Is Right for You?

Vitamin D3 comes in several formats, so the right choice depends on who is taking it, the required dose and which format fits their routine. 

Vitamin D3 Drops

Liquid drops can be a practical choice when a precise, age-appropriate dose is needed. They are commonly used for babies and young children when recommended, and can also suit adults who find tablets or capsules difficult to swallow.

Best suited to: babies and young children when an appropriate product is recommended, and adults who prefer a liquid.

Vitamin D3 Tablets and Capsules

Tablets and capsules offer a straightforward option for adults and older teenagers. They are easy to store and incorporate into a daily supplement routine, with different strengths available to suit different requirements.

Best suited to: adults and older teenagers who prefer a traditional supplement format.

Vitamin D3 Oral Sprays

An oral spray provides an alternative to swallowing a tablet or capsule. It can be particularly useful for adults who prefer a quick, convenient format.

Best suited to: adults who prefer a spray over tablets or capsules.

Vitamin D3 + K2

Some supplements combine vitamin D3 with vitamin K2. Vitamin D contributes to the maintenance of normal bones and normal muscle function, while vitamin K contributes to the maintenance of normal bones.

A combined D3 + K2 supplement isn't necessarily needed by everyone, so consider your individual nutritional needs when choosing a product.

If you take anticoagulant medication or have been advised to monitor your vitamin K intake, speak with your pharmacist or GP before taking a vitamin K-containing supplement.

Best suited to: adults specifically looking for a combined vitamin D3 and K2 formula.

Whichever format you choose, check the vitamin D3 amount per serving and follow the recommended dosage on the product label. 

Vitamin D3 and Winter Immunity: What Does the Evidence Actually Say?

Vitamin D contributes to the normal function of the immune system, as well as the maintenance of normal bones, teeth and muscle function.

This is one reason vitamin D is often discussed during winter, when sunlight exposure is limited in Ireland. However, vitamin D3 supplements should not be presented as a way to prevent colds or flu, and they are not a substitute for other measures that support winter health.

A balanced diet, regular physical activity, sufficient sleep, good hygiene and recommended vaccinations all have an important role to play.

Shop Vitamin D3 & Supplements at Ballyduff Pharmacy

Whether you prefer drops, a spray or tablets, choosing a vitamin D supplement is easier once you know the dose and format that suit your needs. Ballyduff Pharmacy's Vitamins & Supplements and Immunity ranges include several vitamin D options in different formats. 

Metagenics Vitamin D3 + K2 Drops

A liquid D3 + K2 formula in a dropper format for adults who prefer liquid supplementation and are specifically looking for a combination of vitamin D3 and vitamin K2.

One Nutrition D3-Max 3000 IU Vitamin D Oral Spray

An oral spray providing vitamin D3 in a convenient format for adults who prefer a spray rather than tablets or capsules. Check the recommended serving and vitamin D content before use.

Beeline Vitamin D3 + K2 Tablets

A tablet-based D3 + K2 formula for adults who prefer a conventional supplement format and specifically want both nutrients in one product.

Seven Seas Cod Liver Oil Plus Multivitamins

A broader nutritional supplement containing cod liver oil, omega-3 and several vitamins, including vitamin D. It may suit adults and children over 12 looking for a wider range of nutrients rather than a dedicated vitamin D product.

Before adding a vitamin D supplement, check whether your existing multivitamin, cod liver oil or other supplements already contain vitamin D. This can help you avoid unnecessarily combining multiple sources.

[Explore Ballyduff Pharmacy's Vitamins & Supplements]

The Bottom Line

For many people in Ireland, vitamin D supplementation is particularly relevant during the darker months. The right dose and supplementation period depend on factors such as age, skin type and individual circumstances.

Choose an appropriate-strength vitamin D3 supplement in a format that works for you, and speak with your pharmacist or GP if you're unsure what you need.

Disclaimer: This article is intended for general health information and does not replace individual medical advice. If you are pregnant or breastfeeding, taking medication, have an underlying medical condition, have been diagnosed with vitamin D deficiency, or are choosing a supplement for a baby or child, speak with your pharmacist, GP or another qualified healthcare professional. Always follow the dosage instructions on the product label.