health. If you do not know your vitamin D status, the best way to find out is to measure the 25(OH)D levels in your blood. Health reference values for vitamin D are shown here:
| Deficient | < 10 ng/ml |
| Insufficient | 11–19 ng/ml |
| Normal | > 20 ng/ml |
| Optimal | 25–35 ng/ml |
| Excess | > 39 ng/ml |
If the measurement reveals that your 25(OH)D level is low, how much vitamin D supplement should you take? The rule of thumb is that to increase the blood level of vitamin D by 1 ng/ml, you need to take 100 IU; to increase it by 5 ng/ml, you need to take 500 IU; and so on. The suggested dose is for people of normal weight. Obese people need to take 1.5 times more. Wait at least six weeks to see results.
Prevention and Treatment of Diseases
• Prevention. Meta-analysis confirms that vitamin D can help prevent breast cancer (47), lung cancer (82), colorectal cancer (56), blood cancers (45), renal cell cancer (100), bladder cancer (44), melanoma (86), osteoporosis (94), Alzheimer’s disease (37), type 1 diabetes (59), type 2 diabetes (60), rickets (103), lupus erythematosus (83), Parkinson’s disease (96), autism spectrum disorder (42), cognitive impairment (55), fibromyalgia (67), inflammatory bowel disease (79), multiple sclerosis (89), respiratory infection (101), preeclampsia (97), tuberculosis (109), hypertension (78), rheumatoid arthritis (102), fatty liver disease (66), autoimmune thyroid disease (43), depression (58), gestational diabetes (68), obesity (91), orthostatic hypotension (93), Graves’ disease (72), and bone fractures (46).
• Treatment. Meta-analysis confirms that vitamin D can help treat chronic obstructive pulmonary disease (53), lupus erythematosus (83), depression (58), asthma (38), hemodialysis (75), and eczema (62).
Which Food Items Are Vitamin D Rich?
Many animal-based foods contain vitamin D, including fish liver oil, fish, beef liver, and eggs. Milk is also an excellent source of vitamin D. Vegans may consider vitamin D–fortified soy milk and fruit juice.
This list of vitamin D–rich food items is adapted from information provided by the NIH Office of Dietary Supplements.
| FOOD | PORTION | VITAMIN D CONTENT, IU | % DAILY REFERENCE VALUE |
|---|---|---|---|
| Cod liver oil | 1 teaspoon | 1,360 | 340 |
| Swordfish (cooked) | 3 ounces | 566 | 142 |
| Salmon (cooked) | 3 ounces | 447 | 112 |
| Tuna (cooked) | 3 ounces | 154 | 39 |
| Milk | 1 cup | 120 | 39 |
| Yogurt | 6 ounces | 80 | 30 |
| Sardine (cooked) | 3 ounces | 46 | 12 |
| Beef liver | 3 ounces | 42 | 11 |
| Eggs | 1 | 41 | 10 |
| Cheese | 1 ounce | 6 | 2 |
Daily reference value of vitamin D is 400 IU according to the 2013 FDA food-labeling guidelines.
What Are the Recommended Dietary Allowances for Vitamin D?
| 1–3 years | 600 IU |
| 4–8 years | 600 IU |
| 9–13 years | 600 IU |
| 14–18 years | 600 IU |
| 19 years and older | 600 IU |
The upper daily intake limit of vitamin D is 4,000 IU.
Vitamin D Supplements
• Dosage. The most common dosages of vitamin D supplements are 400–5,000 IU, which largely exceed the recommended dietary allowance. Two types of vitamin D supplements are vitamin D2 and vitamin D3. Vitamin D2 comes from plant-based foods and vitamin D3 from animal-based foods. Vitamin D2 and vitamin D3 are similar, although D3 is more potent than D2. Ultraviolet B rays from sunlight trigger the skin to produce vitamin D3, but fish liver oil and deep sea fish are also excellent sources of vitamin D3. Vitamin D supplements in the marketplace predominantly contain vitamin D3.
• Types. Vitamin D supplements can be found as tablets, soft gels, and drops. Vitamin D liquid drops are inexpensive and easy to use. One drop usually contains 400 IU of vitamin D3. If a daily dose of 2,000 IU is needed, just use five drops. Vitamin D is tasteless and odorless, so liquid drops can be added directly to meals or beverages.
• Bone density. Vitamin D regulates the metabolism of calcium and phosphorus ions in the body. Supplementation with vitamin D can enhance the bone density of teenage girls and help postmenopausal women avoid bone loss. The suggested daily dose is 800 IU of vitamin D3.
• Bone fractures. Bone fractures are a major problem for people aged 65 and older. Supplementation with vitamin D can reduce the risk of bone fractures. Studies from Australia have shown that elderly individuals with blood levels of vitamin D in the range of 24–29 ng/ml were the least likely to experience bone fractures, since vitamin D can strengthen bones and muscles. It can also be used by athletes whose blood levels of vitamin D are below 20 ng/ml, which can make them prone to exercise-induced injuries.
• Insulin resistance. Obese individuals whose blood levels of vitamin D are below 20 ng/ml have a 12 times higher risk of insulin resistance compared to individuals of normal weight. Insulin resistance is a major risk factor for cardiovascular diseases, diabetes, and Alzheimer’s disease. Vitamin D supplementation can reduce the risk of insulin resistance in obese individuals.
• Cardiovascular disease. A high level of C-reactive protein in the blood indicates systemic inflammation in the body, which heightens the
