- Stimulating cell and nerve growth.
- Keeping our muscles and joints healthy and fully functional.
- Ensuring our immune systems respond to infections and release antibodies when required.
- Absorbing glucose and calcium from our food: high levels of vitamin D mean greater absorption of these two key substances.
- Balancing the levels of calcium and phosphorus in our bloodstreams.
Vitamin D in foodSome foods are abundant in vitamin D. These include:
FishOily fish like herring, mackerel, sardines and tuna all contain at least 200 international units of vitamin D per piece and upwards – or one quarter to one third of the recommended daily amount. International units, or IU, are a widely recognised metric used to measure biological and medicinal substances.
EggsEggs – or to be more precise egg yolks – also contain a good level of vitamin D. Eggs from free range hens are particularly rich.
Red meatThe amount of vitamin D in red meat varies according to both the particular animal and the amount of sunshine they were exposed to. Clearly this is not a vegetarian-friendly option.
MushroomsMushrooms are the only plant food to offer a good level of vitamin D. Fungi synthesise vitamin D2 when exposed to sunlight. Just like salmon, wild varieties offer much higher levels than farmed ones – as much as 2,300 IU per serving: that’s 300% of the recommended daily amount. By contrast, farmed varieties may offer as little as a few hundred IU. This is because farmed mushrooms are often grown in the dark, under ultraviolet light. Dietary supplements are also available – both multivitamin and specialist – along with cod liver oil, which may not be suitable for vegans but are ideal for those who do not like the taste of fish, or some of the other foods above. Some foods are also routinely fortified with vitamin D – for example, breakfast cereals and some brands of milk. But can you have too much of a good thing? What happens if your diet is too high in vitamin D?
Can too much vitamin D be bad for you?Too much vitamin D can potentially be damaging to your health, however this is rare. It is highly unlikely that you could ever overdose on Vitamin D via sunlight or through your diet. The amount of cholecalciferol produced by our bodies is regulated by our nervous systems. In some rare cases, a toxic build-up of vitamin D is triggered by the overuse of dietary supplements, causing someone to exceed the recommended daily intake for a prolonged period. Excessive sunbed use is also a potential risk factor. Our bodies store vitamin D within fatty organs like the liver for later use, so previously consumed vitamin D may also contribute to toxic build-up.
How much is too much?There is no precise answer to this question as blood levels and nutrient requirements vary by individual. But most doctors would agree that a blood level of 150 nanograms per litre (ng/ml), or a dietary intake of in excess of 4,000 IU per day, would be hazardous to the health of most adults. 4,000 IU is more than six times the recommended daily amount of 600 IU. However, it is worth reiterating that overdosing on vitamin D is unlikely.
Vitamin D toxicityExcessive vitamin D absorption is medically termed hypervitaminosis D. This condition throws the balance of calcium circulating within our system out of balance, causing an excess to begin accumulating. Doctors refer to this state as hypercalcemia. Hypervitaminosis D is not common but it can cause health complications. Typical symptoms include:
- Vomiting and nausea
- Mental confusion
- Physical weakness
- Kidney problems and kidney stones
- Pain in particular bones as growth and repair is disrupted
Are there any risks to taking vitamin D supplements?As previously mentioned, it’s highly unlikely that exposure to vitamin D through sunlight or through your diet will result in an overdose. However, it is possible to take too many supplements which contain vitamin D. Doing so can increase the levels of calcium in your blood (hypercalcemia), which can result in nausea, constipation, lightheadedness, and confusion. As this is rare it is easy to avoid. Ensure you know the dose of any supplements you might take, sticking to the recommended daily amount. If you take multiple supplements, especially multivitamins, make sure you’re not doubling up on anything. Additional care is needed in some instances when taking vitamin D supplements:
- If you take certain medicines, such as digoxin or thiazide diuretics
- If you have high calcium levels, certain types of cancer, or other medical conditions including kidney stones, kidney disease, or liver disease
What to do if you have an excess of vitamin D – can it be flushed out?Cutting your intake of vitamin D and calcium is the most important step to take if your consumption has become excessive. Allow your system to settle and rebalance itself. But how do you flush vitamin D out of your system – and can you even do that? Yes, by ensuring you consume plenty of water. This will encourage urination, allowing your body to shed the excess vitamin D and calcium more quickly. Prescription diuretics like furosemide can also be helpful. A diuretic is a medicine that increases fluid loss.
Low levels of vitamin DWhile elevated vitamin D levels are exceptionally rare, it’s far more common for somebody to experience low levels of vitamin D.
Symptoms of low vitamin D levels include: