Vitamin D

Why vitamin D is good for you

Vitamin D’s most important role is to regulate how much calcium is absorbed from the food that is eaten and to ensure that levels of calcium are regulated properly in the body.

The immune system also needs vitamin D to function effectively.

To get enough vitamin D, a general rule of thumb is: in winter, get about 20-30 minutes a day of sunlight directly on the face and in summer, 10-20 minutes (but not in the hottest part of the day).

The ultraviolet light in sunshine makes a type of cholesterol that is found just under the skin, into cholecalciferol (or vitamin D3). The vitamin D3 gets carried to the kidneys, where it becomes even more active. Some of the vitamin D stays in the liver and kidneys, where it helps to reabsorb calcium from the blood. Some goes to the bones to help them hold onto their calcium. The rest goes to the intestines to help absorb calcium from food.

Vitamin D is found naturally in some foods, in a slightly different form, called ergocalciferol or vitamin D2. The body can use this form of vitamin D just as well as the other type from sunshine.

Important vitamin D facts

• Cod liver oil was the main source of vitamin D for a long time.
• Fish oil contains a lot of Vitamin D, which is in fish liver, mackerel, herring, sardines, salmon, tuna and other oily fish
• Today, vitamin D is added to milk as well as to breakfast cereals
• Vitamin D is fat soluble, so when a lot is made, by spending a day at the beach, some of it gets stored in the fatty tissues and in the liver
• Vitamin D is also classified as a hormone
• There is a receptor for vitamin D on every cell in the body, which means that it is important for metabolic processes on a cellular level
• People who have adequate to high levels of vitamin D in the body outlive people with low to deficient levels

Vitamin D works best with

• Vitamin A
• Boron
• Calcium
• Magnesium
• Phosphorus
• Potassium
• Chondroitin
• Glucosamine

Vitamin D and health

• Cancer – it is has been known for a long time that colon cancer and breast cancer are more common among people in northern climates – places where that are very cold and do not get much sun for part of the year. There appears to be a connection between risk for colon cancer and low sunshine exposure. According to recent studies, people who get a lot of vitamin D from their food and supplements are much less likely to get colon cancer. To get vitamin D protection, only 200IU is required daily – the amount in two cups of milk. Is the same protection given by sunshine? Yes. But the vitamin D from sunshine is difficult to quantify. Vitamin D not only helps prevent cancer, it can also help treat it. The powerful anti-cancer drug tamoxifen, which is widely used to treat cancer of the ovaries, uterus and breast (in women) seems to work even better when it is combined with small doses of vitamin D
• General health – studies show that there is a receptor for vitamin D on every cell in the body and that people who have enough vitamin D die less frequently from any cause compared to people who are low to deficient in this very important vitamin
• Immune system – vitamin D can help strengthen the immune system in general
• Psoriasis – psoriasis is a chronic skin disease that makes the skin get itchy, red, flaky patches. Sunshine seems to clear up the patches for some people. Likewise, a prescription cream that has vitamin D in it seems to help too. Just taking a lot of vitamin D in supplements does not help psoriasis – and it could be dangerous
• Better hearing – in some cases of hearing loss, a shortage of Vitamin D may have damaged the delicate ear bones – and it is possible that taking Vitamin D supplements can help restore some hearing

Talk to a medical professional about vitamin D supplements before taking them.

Groups at risk of vitamin D deficiency

Deficiency can occur in individuals that do not get enough sunlight.

People that may be deficient in vitamin D include:

• People who don’t get much sunlight – people who are house-bound or are in nursing homes are especially at risk of vitamin D deficiency
• Older adults – older people need more vitamin D in general, because they are making about half as much vitamin D as younger adults do
• People with kidney or liver disease – cannot convert vitamin D3 into its more active form
• People taking certain drugs – people taking corticosteroids (deplete vitamin D), cholesterol-lowering (block vitamin D) or anticonvulsant drugs (interfere with vitamin D usage) should talk to a medical professional about supplements
• Alcoholics – alcohol blocks the ability to absorb and store vitamin D so people who drink a lot of alcohol may be deficient

Talk to a medical professional about vitamin D supplements before taking them.

Symptoms of vitamin D deficiency

Children who do not get enough vitamin D develop rickets – their bones do not grow and do not harden properly. Luckily, most children do get enough vitamin D in their diet and rickets is very rare today in the West, but it does still occur in developing countries.

Vitamin D deficiency in older adults shows up as a condition called osteomalacia – soft, weak and painful bones.

Vitamin D in food

Vitamin D recommended daily intake (RDI)

The tolerable upper limits should only be taken for short periods and only under medical supervision.

Overdosage, toxicity and cautions for vitamin D

Too much Vitamin D from supplements is dangerous! Do not exceed 2,000IU (50mcg) daily – for adults and 1,000IU (25mcg) – for infants and children!

Symptoms of having too much vitamin D are:

• raised calcium levels
• lowered appetite
• increased thirst
• nausea
• vomiting
• drowsiness
• abdominal pain

A long-term effect of too much vitamin D is the deposit of calcium in soft tissues of the body including the blood vessel walls and kidneys where it can cause serious damage.

References

• Cooper GS, Umbach DM. Are vitamin D receptor polymorphisms associated with bone mineral density? A meta-analysis. J Bone Mineral Research, 1996. 11(12):1841-9
• Dawson-Hughes B, Haris SS, Krall EA, Dallal GE. Effect of Calcium and Vitamin D Supplementation on Bone Density in Men and Women 65 Years of Age or Older. New England Journal Of Medicine, 1997. Volume 337 (10): 670-676
• Gloth FM, Gundberg CM, Hollis BW, Haddad JG, Tobin JD. Vitamin D deficiency in homebound elderly persons. JAMA 1995. Vol 274(21)
• Pfeifer M, et al. Effects of a Short-Term Vitamin D and Calcium Supplementation on Body Sway and Secondary Hyperparathyroidism in Elderly Women. Journal of Bone and Mineral Research, 2000. Vol15 (6)
• Office of Dietary Supplements USA – has the official USA RDI for all vitamins (these are also adopted by Australia), accessed 9 August 2005
• Osiecki, Henry, The Nutrient Bible 2002, BioConcepts Publishing
• Yoshizawa C, et al. Mice lacking the vitamin D receptor exhibit impaired bone formation, uterine hypoplasia and growth retardation after weaning. Nature Genetics 1997. Vol 16, 391-396

Last reviewed and updated: 9 May 2024