Ask an Irish GP what single nutritional supplement they most commonly recommend, and the answer, overwhelmingly, is Vitamin D. Ask an Irish dietitian the same question, and you will likely get the same answer. It is not a trend or a fad — it is a response to a clear and well-documented public health reality: Ireland does not get enough sunlight for most of its population to produce adequate Vitamin D, for much of the year, from sunlight alone.
For bone health specifically, Vitamin D is not optional. Without it, the body cannot properly absorb calcium from the gut — regardless of how much calcium you eat. And without adequate calcium absorption, bone density declines. It is a straightforward chain of consequences with a straightforward prevention.
Why Ireland Is Different
The body produces Vitamin D through a photochemical reaction in the skin triggered by UVB radiation from sunlight. This mechanism works well in countries closer to the equator, where the sun is high in the sky and UVB rays reach the surface reliably for most of the year.
Ireland, situated between 51°N and 55°N, is at a latitude where UVB radiation is insufficient for meaningful Vitamin D synthesis from approximately October to March. During these months — which account for roughly half the year — the sun is too low in the sky for the relevant wavelengths to reach Earth's surface in Ireland. No amount of time outdoors will generate Vitamin D production during this period.
Even during the spring and summer months (April to September), Ireland's famously cloudy weather means that on many days, UVB levels are insufficient for adequate synthesis. The TILDA study — the Irish Longitudinal Study on Ageing, one of the most comprehensive studies of health in older Irish adults — found that over a quarter of adults aged 50 and over in Ireland were Vitamin D deficient, and a much higher proportion had insufficient (rather than optimal) levels.
What the Evidence Says About Supplementation
The evidence for Vitamin D supplementation in the prevention of fractures is clearest in older adults, particularly those who are deficient or at risk of deficiency. Large meta-analyses of randomised trials have shown that combined Vitamin D and calcium supplementation reduces fracture risk — particularly in institutionalised older adults and those with documented deficiency.
The evidence is more nuanced for the general population without confirmed deficiency. Some more recent large trials (including the VITAL trial in the US) found that high-dose Vitamin D supplementation in people who were not already deficient did not significantly reduce fracture risk. This suggests that supplementation is most important for people who are actually deficient — which, in Ireland, is a substantial proportion of the adult population.
The practical implication for people in Ireland: routine supplementation of 10 micrograms (400 IU) per day is reasonable and recommended for most adults, particularly October to March. For older adults, people who are housebound, and those with osteoporosis, higher amounts (15–20 micrograms, or 600–800 IU) are often recommended by GPs — always discuss with your own doctor.
Food Sources: Helpful but Not Enough
Vitamin D is found in a relatively small number of foods. The best natural sources are oily fish — salmon, mackerel, herring, sardines — which can provide meaningful amounts per serving. Egg yolks and liver also contain Vitamin D, in smaller quantities. Some foods in Ireland (certain margarines, breakfast cereals, and plant milks) are fortified with Vitamin D, which is worth checking on food labels.
But even a diet rich in these foods is unlikely to provide the 10–15 micrograms per day that most adults need in winter. A 100g serving of Atlantic salmon might provide around 15–20 micrograms — close to a full day's requirement — but most people do not eat oily fish daily. For most Irish adults, supplementation is the practical solution to a structural dietary shortfall.
Sun Exposure: A Summer Strategy Only
During the Irish summer — primarily May to August on clear or partly cloudy days — short periods of direct sun exposure can contribute to Vitamin D production. Around 10–15 minutes of midday sun on the arms and face, without sunscreen, on a reasonably sunny day, can generate useful amounts for fair-skinned people.
After this brief period, it is sensible to apply sun protection. Importantly, the body cannot store UV exposure as “banked” Vitamin D for winter — the conversion happens in real time, and once made, Vitamin D is stored in fat tissue for weeks or months, but not indefinitely. This is why consistent supplementation throughout the winter months is more reliable than relying on summer sun.
A Simple Recommendation
If you live in Ireland, are an adult over 18, and do not have a medical condition that affects Vitamin D metabolism, the following is broadly consistent with current Irish guidance:
- Take a daily supplement of 10 micrograms (400 IU) of Vitamin D3
- Take it year-round, or at minimum October to March
- If you are over 65, housebound, or have osteoporosis, discuss whether a higher dose is appropriate with your GP
- Do not take more than 100 micrograms (4,000 IU) per day without medical supervision
For the majority of people, this is a safe, cheap, and evidence-supported step. Combined with adequate calcium from diet (and supplementation where needed), regular weight-bearing exercise, and — if appropriate — bone-protective medication, it forms an important part of maintaining bone health in the Irish climate.
For full guidance, see our dedicated Vitamin D page and Nutrition & Calcium page.