Vitamin D

Vitamin D is essential for bone health — without it, your body cannot properly absorb calcium, no matter how much you consume. In Ireland, Vitamin D deficiency is common due to our northern latitude and limited sunlight for much of the year.

Why Does Vitamin D Matter for Bones?

Vitamin D promotes the absorption of calcium from the intestine. Without adequate Vitamin D, only 10–15% of dietary calcium is absorbed, compared to 30–40% when Vitamin D levels are sufficient. Low Vitamin D also causes the body to increase secretion of parathyroid hormone (PTH), which draws calcium out of the bones — accelerating bone loss.

Vitamin D deficiency has also been linked to increased fall risk, as it plays a role in muscle strength and neuromuscular function. This adds to its importance for fragility fracture prevention.

The Irish Sunlight Problem

The main natural source of Vitamin D is sunlight — specifically, UVB radiation triggers Vitamin D synthesis in the skin. Ireland is located at latitudes between 51°N and 55°N. At these latitudes:

• UVB radiation is insufficient for Vitamin D synthesis from approximately October to March
• Even in summer, cloudy or overcast weather (very common in Ireland) can prevent adequate synthesis
• Vitamin D produced in the skin during summer months is stored in fat tissue, but this may not be sufficient to last through winter for many people
• Older skin is less efficient at producing Vitamin D from sunlight

This is why dietary intake and supplementation are critically important for people living in Ireland.

How Much Vitamin D Do You Need?

Based on FSAI recommendations. Higher doses may be recommended for people with osteoporosis, those with confirmed deficiency, or those on bone-protective medications — always discuss with your GP.

Food Sources of Vitamin D

Very few foods naturally contain significant amounts of Vitamin D. Those that do include:

• Oily fish — salmon, mackerel, sardines, herring, trout (highest natural sources; 85g salmon provides approximately 15–20 micrograms)
• Egg yolks — modest amounts (approximately 1–2 micrograms per yolk)
• Liver — a good source, but not recommended in large amounts for pregnant women due to Vitamin A content
• Fortified foods — some margarines, cereals, and plant milks are fortified with Vitamin D; check the label

Food sources alone are rarely sufficient to meet Irish adults' Vitamin D needs, particularly in winter.

Should I Take a Supplement?

The short answer, for most people in Ireland, is yes — at least from October to March. Many Irish GPs and the FSAI recommend:

• A daily supplement of 10 micrograms (400 IU) of Vitamin D3 for the general adult population, year-round or at minimum October–March
• Older adults (65+) may need 15–20 micrograms (600–800 IU) daily
• People with osteoporosis who are taking bone medication are almost always prescribed Vitamin D (and calcium) supplementation alongside it

Vitamin D3 vs D2

There are two main forms of Vitamin D in supplements: D3 (cholecalciferol) and D2 (ergocalciferol). Vitamin D3 is more effective at raising and maintaining blood Vitamin D levels and is the preferred form. Most supplements available in Ireland contain D3.

Who Is at Particular Risk of Vitamin D Deficiency?

The following groups should pay particular attention to Vitamin D:

• Older adults — skin becomes less efficient at producing Vitamin D with age; older adults may also spend less time outdoors
• Housebound individuals or those in care — little or no outdoor exposure
• People who cover their skin for cultural or religious reasons
• People with darker skin tones — more melanin means lower Vitamin D synthesis from the same sun exposure
• People with obesity — Vitamin D is fat-soluble and can be sequestered in fat tissue, reducing circulating levels
• People with malabsorption conditions (coeliac disease, IBD, following bariatric surgery)

Sun Exposure: A Practical Guide

During the Irish summer months (approximately April to September, particularly May to August on clear days), short periods of sun exposure can contribute to Vitamin D production:

• Aim for approximately 10–15 minutes of midday sun (11am–3pm) on arms and face, without sunscreen
• This should be enough for most fair-skinned people to produce a useful amount of Vitamin D
• After this short exposure period, apply sun protection as usual to protect against skin cancer
• Do not burn — burning increases skin cancer risk without additional Vitamin D benefit

Remember: even in summer, cloudy Irish weather means sun exposure is often inadequate. Do not rely on sun alone to meet your Vitamin D needs throughout the year.