All About Vitamin D

Summary: Vitamins, by definition, are not produced by the body. Vitamin D is in fact a hormone produced when UVB (290nm – 310nm) rays convert the cholesterol in skin into this form. It is stored in the liver, from where it is released into the kidneys, before becoming active in the blood stream. Critical for the absorption of calcium and phosphorus, it helps maintain bone health. Research show it’s critical in fighting over 15 different kind of cancers.

Despite plentiful sunlight, a large population is deficient as people proactively avoid sun. However, large part of North America (regions north of Phoenix, AZ or Bakersfield, CA) doesn’t receive the UVB rays from Nov to Mar as they are blocked by the ozone layer.

Vitamin D toxicity is extremely rare. Fortified foods or supplements are very popular to make up for any deficiency. Medical professionals recommend maintaining levels of at least 20-30 ng/ml, which can be tested with an easy and simple at-home Vitamin D test kit.

Vitamin D healthy levels

What is Vitamin D?

All About Vitamin D

Vitamins, by definition, are compounds that are not produced by the body. However, the UVB rays (290-310 nm) in sunlight convert a form of cholesterol in the skin into Vitamin D. It is stored in the liver–like water in a camel’s hump–until it is released into the kidneys which make the final active form that circulates in the blood. It is crucial for absorption of calcium and phosphorus–minerals essential for maintaining healthy bones, especially in children and elderly. In recent years, research has shown that Vitamin D is essential for fighting over 15 different kind of cancers.


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Despite abundant sunlight, a large population is Vitamin D deficient. That is because people proactively try to avoid exposure to sun. Another problem is that a large part of North America (regions north of Phoenix, AZ & Bakersfield, CA & Charlotte, NC) doesn’t receive the UVB rays in winter months from Nov to Mar as they are blocked by the ozone layer. Fortified foods fortified and supplements are therefore popular sources to make up for any deficiency.
Medical professionals recommend maintaining levels of at least 20-30 nL/ml, which can be tested with a simple blood test using an at home Vitamin D test kit. Toxicity is extremely rare but those taking the supplements should monitor their levels regularly.

What are the types of Vitamin D?

  • D3 (cholecaliciferol) – this form is naturally produced by the body; it is rarely toxic as higher levels (>20 kIU) are removed by the body; it is the most common type found in supplements
  • D2 (ergocalciferol) – this form is produced in plants & fungi but not in humans; however, most prescriptions contain D2 but it is half as effective as D3

What are some of the most interesting properties of Vitamin D?

  • Not really a vitamin but a hormone (by definition Vitamins are essential but not produced by the body; Vitamin D surely is!)
  • Fat soluble: overweight & obesity will prevent release into body
  • Rarely toxic with high dose (does more sunlight cause toxicity?)

What is Vitamin D needed for?

It is needed for calcium and phosphorus absorption in the body. Deficiency can have serious health impact:

  • Children: Rickets (weak, improper formation of bones)
  • Adults: Osteomalacia (low bone density, unhealthy bone repair, maintenance due to improper Ca, P absorption)
  • It is also known to be crucial for preventing, reducing multiple cancers (including cancers of breast, lung, colon, prostate); critical for cardiovascular health, bone fracture & fall, diabetes, stress & fatigue, and other common diseases

Vitamin D and risk of cardiovascular disease

Other key uses of Vitamin D?

  • Body has 26 Vitamin D responsive tissues that require adequate levels to activate their functions affects over 200 genes in the body
  • Excess 25-D can be metabolized to 1,25-D3 in other cells and tissues besides kidneys

How does Vitamin D metabolism happen in the body?

  • Step 1: Sun (i.e., UVB rays) hits the skin and a type of cholesterol called 7-dehydrocholesterol (7-D) is activated
  • Step 2: 7-D becomes pre-Vitamin D & immediately becomes Vitamin D3
  • Step 3: Vitamin D3 becomes 25-D in liver through hydroxylation and stores in liver (like a camel’s hump storing water)
  • Step 4: 25-D is released, as needed, to kidneys where it becomes an active and potent form called 1,25-D3; this form circulates in the body and maintains the amount of calcium; 1,25-D3 is the right form of Vitamin D to monitor; multiple cells and tissues have receptors to convert 25-D to 1,25-D3, thus critical in other parts of body

Metabolism happens through regular method and in the cells:

  • Regular metabolism:
    Liver(25-D) –> into bloodstream –> kidneys(1,25-D3: active, vital form) –> into bloodstream –> intestinal cells (absorption of Ca, P –> healthy bones)
  • Autocrine cell functions (metabolism in the tissues and cells, a role discovered based on research in past 20-25 years):
    Liver(25-D) –> most organs of body with Vitamin D receptors(1,25 D3: active, vital form) –> utilized by cells & tissues (essential for preventing cancers & other diseases)

Vitamin D and cardiovascular risk

What prevents people from getting enough Vitamin D (and soaking the sun)?

  • Fear of skin-cancer
  • Aging
  • Wrinkled skin
  • Discoloration of skin

What are the sources of Vitamin D?

  • Sunlight (UVB: 290nm – 315nm wavelength, deep violet)
  • Fish liver oil (cod-liver, salmon)
  • Supplements
  • Tanning beds
  • Fortified food (milk, orange juice, cereals, margarine, etc.)
  • Most food items don’t have Vitamin D or barely have any

Sun as a source of Vitamin D

  • UVB rays [very narrow band of 290-315nm wavelength; visible light is 360nm(violet) -780nm(red)] are main source that activate Vitamin D; but can’t penetrate as deep; even window glass will block it
  • UVA rays (>315nm wavelength) penetrate deeper but do not prompt skin to make Vitamin D; cause wrinkles, aging, skin discoloration

How much sun do you need?

  • Find the time it takes for the skin to turn pink (depends on skin tone, time of day, season, etc.)
  • 25-50% of this time will give 1,000 IU
  • try few times a week in summer to get sufficient dose of UVB and let it store in liver

What is the measurement unit of Vitamin D?

  • Unit in food & other sources: IU (International Unit); 1000 IU = 25 microgram of Vitamin D (for other Vitamins, microgram/IU can be different). This is the unit you see on Vitamin D supplements. A 2,000 daily dose is basically 50 microgram.
  • Unit when measured in the blood: ng/ml (1 ng/ml = 2.5 nmol/l). This is what you will see when tested using an at-home Vitamin D test kit.

How much Vitamin D do you need?

  • Recommended daily allowance (RDA) as per the government direction are:
    • 50 years or younger: 200 IU per day
    • Over 50 years: 400 IU per day
    • Upper safe limit: 2000 IU/day**Most medical professional recommend 5-10 times higher dose and are asking government to revisit these limits setup in 1997 (note 30 minutes of full Sun exposure gives as much as 20,000 IU!!)

How much Vitamin D do you get from each source?

  • From Sun: 12 minutes at noon with bare arms & legs for a white woman – 3000 IU; 30 minutes – 20,000 IU (people with darker skin will need more since the melanin in skin will absorb some of the sun)
  • From Cod-liver: best natural food source at 1360 IU per tablespoon (but watch out for excess Vitamin A in it which can be toxic!)
  • Fortified food: 85% of winter supply
    • US: milk, cereals, orange juice, margarine
    • Canada: only milk and margarine
    • Even fewer options for those who are lactose intolerant or vegetarian or vegan

What are key food sources of Vitamin D?

  • Cod-liver oil: 1360 IU in 1 tablespoon
  • Salmon: 360 IU (3.5 oz, cooked)
  • Mackerel: 345 IU (3.5 oz, cooked)
  • Sardines: 250 IU (1.75 oz, canned in oil)
  • Tuna fish: 200 IU (3 oz, cooked)
  • Milk: 98 IU (fortified, 1 cup; you need 10 cups for 1,000 IU!!)
  • Margarine: 60 IU (1 tablespoon, fortified)
  • Egg: 20 IU (one egg with yolk)
  • Beef: 15 IU (3.5 oz)
  • Cheese: 12 IU (1 oz)
  • Tanning beds: helpful but are known to cause skin cancers & generally not recommended; otherwise same exposure advise as for Sun: 25-25% of time it takes to turn your skin pink
  • Multivitamins: Okay to use but note overdose of other vitamins can be toxic (e.g., Vitamin A is known toxic)

What are the factors affecting Vitamin D intake?

Environmental factors

  • Latitude – i.e., how far from equator. Larger distance means UVB rays go through a longer ozone layer and get absorbed more. Beyond 35 degrees latitude north or south, almost no UVB reach the surface from Nov to March (regions north of Flagstaff AZ, Albuquerque NM, Knoxville TN, Oklahoma city OK, Charlotte NC). For reference, Canadian border is at 49th parallel and Salem OR is at 45th parallel.
  • Altitude – i.e., height above see level. Lower altitudes absorb more UVB and make less of it. People in mountains get more UVB.
  • Season of the year – Winter months get less sun.
  • Time of the day – need UV Index of 3 or more; 10 am – 2 pm are best times.
  • Air pollution – particles absorb UVB and reduce the production.
  • Cloud cover blocks the sun; the US Pacific Northwest region with long rainy periods will get less sun and thus lower production in skin

Personal factors affecting Vitamin D intake

  • Sunscreen/sunblock – absorb the sunlight and hence prevent the body in making it; higher SPF means more sun is blocked (e.g., SPF8: 92% skin’s production is blocked; SPF15: 99% blocked); it’s advised to soak sun for few minutes before applying sunscreen
  • Melanin – darker skin has higher melanin which absorbs more sunlight and competes with Vitamin D production; African people need almost 10 times more UVB exposure
  • Age – older people have less 7-D in the skin and need almost 25-50% more sunlight
  • Weight – Vitamin D is fat soluble; fat cells in skin will dissolve making less of it available for tissues and organs
  • Clothing – body coverage blocks sunlight; e.g., Islamic women & men, people in cold places with more body coverage will get less sun exposure

What are the reasons for low awareness and deficiency of Vitamin D?

  • Considered a new fad
  • New roles of Vitamin D are discovered only recently in past few decades
  • Awareness of skin cancer from sunlight is much higher
  • Perception that inadequate sun exposure only impacts childhood growth
  • Symptoms are subtle and can be confused with other medical conditions

What are the symptoms of Vitamin D deficiency?

  • Muscular weakness (weak muscles)
  • Feeling of heaviness in the legs
  • Chronic musculoskeletal pain (chronic pain in muscles and bones)
  • Fatigue or easy tiring
  • Frequent infections
  • Depression
  • Chronic pains, e.g., back pain, neck pain (defect in bone-hardening with deep, gnawing pain in muscles and bones)

What causes low Vitamin D?

  • Low levels in children: due to reduced outdoor activities and sunscreen protection
  • Pregnant and nursing mothers: due to sharing with baby
  • Obese and overweight: Vitamin D dissolves in fat and therefore fat cells can absorb and store, making less of it available
  • Elderly: less Vitamin D precursor in skin (may need up to 4x Sun otherwise can result in weaker bones and fractures)
  •  Others: People with Crohn’s disease, cystic fibrosis, gastric-bypass surgery, liver or kidney failure might not be able to absorb fat soluble Vitamin D
  • Vitamin D levels
    • Deficient: 10-20 ng/ml
    • Insufficient: 20-30 ng/ml
    • Normal: > 30 ng/ml — recommended to maintain 30-40 ng/ml; medical professionals recommend to error on the higher side
    • Overdose: 40-70 ng/ml
    • Toxic: > 150 ng/mlVitamin D Test: Measurement unit for blood test: ng/ml (1 ng/ml = 2.5 nmol/l)

Vitamin D and obesity

How to get tested for Vitamin D?

  • The most popular test for Vitamin D is using a blood sample. You can order an at-home Vitamin D test kit that can accurately measure the active form of Vitamin D (1,25-D3) in blood stream. The kit can be ordered online & a blood sample can be provided from home without the need to visit a doctor or any labs. The comprehensive lab report will clearly explain your results.
  • More comprehensive but expensive test is LC-MS/MS (liquid chromatography tandem mass spectroscopy)

Why to get tested for Vitamin D?

  • Despite all the awareness, a significant part of the population is deficient. Without getting tested, it is very difficult to tell the levels. Those working indoors do not get enough exposure to sun and end up being deficient.
  • Symptoms are subtle and can be confused with other medical conditions.
  • It has been shown to play a key role in fighting over 15 different kinds of cancers and new research suggests it is important for other key roles and not just for bone health.
  • Those with darker skin need even more sun since the melanin in skin competes for sunlight. People from Africa, South East Asia, Latin and South America tend to believe deficiency is a problem only for people with fair skin. However, their darker skin color has naturally evolved for high sun exposure and when they live in regions farther away from equator their requirement for sun exposure increases as these regions get less sunlight.
  • During winter, when the sun is not directly above us, sunlight travels a longer path through the atmosphere. Therefore, more of the UVB rays are absorbed by the ozone layer and the remaining sunlight can not produce as much on exposure to skin. In fact, regions north of 35th parallel (north of Phoenix, Bakersfield, Albuquerque, Knoxville, Oklahoma City, Charlotte, Raleigh) get almost no UVB from Nov to Mar.
  • Glass windows, sunscreens block the Vitamin D producing part of the sunlight. Although people think they are getting the sun in their house but this filtered light produces almost none of it.
  • Children need calcium and phosphorus for developing their bones and it plays a key role in absorbing these minerals.
  • As we age, our bone density decreases and we require higher levels for maintaining healthy bones. It has also been shown to reduce fractures among elderly.
  • It dissolves in fat cells. Therefore, obese and overweight people need more to compensate.
  • Few naturally occurring food items contain Vitamin D. For vegetarian and vegan diets, the choices are extremely limited. Therefore, it is always a good idea to test your Vitamin D levels before starting any supplements. An at-home Vitamin D test kit is inexpensive and simple way to get tested.

What are the annual recommended tests?

  • November: onset of Vitamin D winter (fall)
  • March: end of winter (spring)

What are suggested supplements for Vitamin D?

What physicians normally suggest (confirm with your physician before starting any of these regimens):

  • A 1,000 IU daily dose will increase levels in blood by 10 ng/ml in 3-4 months
  • If levels < 20 ng/ml, then 50 kIU/week for 8 weeks –> then change to 2,000 IU per day
  • If levels are 20-30 ng/ml: same as < 20 ng/ml
  • If levels are 30-40 ng/ml: 50 kIU/week for 6 weeks –> then change to 2,000 IU per day
  • Unborn babies: pre-natal vitamins have 400 IU
  • Breast feeding babies: 400 IU/day (nursing mothers need > 40 ng/ml and may need up to 4,000 IU/day)
  • Younger than 1 year: 400 IU/day
  • 1-2 year old: 1,000-2,000 IU/day (based on weight
  • Over 12 years old: 2,000 IU/day

What are overdose concerns of Vitamin D?

  • Excess Sun or skin based overdose is naturally protected by the body.
  • Overdose toxicity of 150 ng/ml can only be achieved by several months of >10,000 IU/day; very hard to get this level of overdose.
  • In reported literature, one case of overdose with 150,000 IU/day taken over two years resulting in 500 ng/ml but patient stopped taking and didn’t have any immediate health conditions

What are the overdose symptoms of Vitamin D? Side effects of Vitamin D?

Overdose (>150 ng/ml) results in elevated calcium in blood that can cause:

  • Abdominal pain
  • Constipation
  • Muscle weakness
  • Itching
  • Vomiting
  • Extreme thirst
  • Predisposition to kidney stones and high blood pressure

Who should not take Vitamin D?

High levels of Vitamin D are not recommended for:

  • Patients with granulomatous diseases (Tuberculosis and Sarcoidosis) – keep 20-30 ng/ml
  • Patients with Lymphomas
  • Those taking drug called hydrochlorothiazide (mild diuretic) for high blood pressure (this raises Ca level and might further increase to cause kidney stones)
  • Drugs that lower Vitamin D levels (drugs for seizures; cimetidine, steroids, certain asthma medicines, and weight loss drugs)


Source: Vitamin D Revolution by Soram Khalsa, M. D.

For more information & references, visit the NIH page on Vitamin D

Disclaimer: For information purposes only—not to be used for diagnosis or to replace advice from a medical professional. Information on other health tests can be found here., an At Home Vitamin D Test can be ordered here. You can order a CLIA-certified at-home health test from anytime for free shipping and physician-approved reports.