Vitamin D in food

 Vitamin D (calciferol) is a fat-soluble vitamin that is found naturally in a few foods, added to others, and available as a dietary supplement. Endogenous production occurs when ultraviolet (UV) rays from sunlight strike the skin and initiate vitamin D synthesis.

Vitamin D obtained from sunlight, foods, and supplements are biologically inactive and require two hydroxylations in the body to be activated. The first hydroxylation occurs in the liver and converts vitamin D to 25-hydroxyvitamin also known as "calcidiol," while the second occurs primarily in the kidney and results in the physiologically active 1,25-dihydroxyvitamin also known as "calcitriol". 

Vitamin D aids calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations, allowing normal bone mineralization and preventing hypocalcemia tetany (involuntary contraction of muscles, leading to cramps and spasms). It is also required for osteoblasts and osteoclasts to grow and remodel bone. Bones can become thin, brittle, or misshapen if vitamin D levels are low. Sufficient vitamin D prevents rickets in children and osteomalacia in adults. Vitamin D, along with calcium, helps protect older adults from osteoporosis.

 

Recommended Amounts

In healthy people, the Recommended Dietary Allowance for vitamin D provides the daily amount required to maintain healthy bones and normal calcium metabolism. It assumes very little sun exposure.

RDA: The Recommended Dietary Allowance for adults 19 and older is 600 IU (15 mcg) daily for men and women, and 800 IU (20 mcg) daily for adults over 70.

Many people may fall short of the vitamin minimum requirement., the median daily intake of vitamin D from food and supplements in women aged 51 to 71 years was 308 IU, but only 140 IU from food alone (including fortified products). An estimated 1 billion people worldwide have insufficient vitamin D levels in their blood, and deficiencies can be found in all ethnicities and age groups.

Doctors in developed countries are seeing a resurgence of rickets, a bone-weakening disease that had been largely eradicated through vitamin D supplementation. There is scientific disagreement about how much vitamin D people need each day and what serum levels are optimal for disease prevention.

The Institute of Medicine (IOM) issued recommendations in November 2010 to increase the daily vitamin D intake for children and adults in the United States and Canada to 600 IU per day.  The upper limit was also raised from 2,000 to 4,000 IU per day in the report. Although some organizations, such as The Endocrine Society, recommend 1,500 to 2,000 IU daily to achieve adequate serum vitamin D levels, the IOM concluded that there was insufficient evidence to establish a cause-and-effect relationship between vitamin D and health benefits other than bone health. Since then, new evidence has supported other benefits of consuming an adequate amount of vitamin D, though there is still disagreement about what amount is considered adequate.

Signs of Deficiency and Toxicity

Vitamin D deficiency can result from a lack of vitamin D in the diet, poor absorption, or a metabolic need for higher amounts. A deficiency may occur if one does not consume enough vitamin D and does not receive enough ultraviolet sun exposure over an extended period of time (see section above). People who cannot tolerate or do not consume milk, eggs, or fish, such as those with lactose intolerance or who follow a vegan diet, are more likely to be deficient. Other people who are at high risk of vitamin D deficiency are:

People suffering from inflammatory bowel disease (ulcerative colitis, Crohn's disease) or other conditions that impair fat digestion. Vitamin D is a fat-soluble vitamin that is dependent on the ability of the gut to absorb dietary fat.

Obese people have lower levels of vitamin D in their blood. Vitamin D accumulates in excess fat tissues but is difficult for the body to use when needed. To achieve a desirable blood level, higher doses of vitamin D supplementation may be required. When obese people lose weight, their blood levels of vitamin D rise.

People who have undergone gastric bypass surgery typically remove the upper part of the small intestine where vitamin D is absorbed.

Toxicity 

The most common cause of vitamin D toxicity is supplementation. The vitamin's low levels in food are unlikely to reach toxic levels, and excessive sun exposure does not cause toxicity because excess heat on the skin prevents D3 formation. It is not recommended to take more than 4,000 IU of vitamin D per day unless under the supervision of your doctor.

Symptoms of toxicity

• Anorexia
• Irregular heartbeat
• Weight loss
• Hardening of blood vessels and tissues due to increased blood levels of calcium, potentially leading to damage to the heart and kidneys

Here are the Top 5 food which is rich in Vitamin D

Raw Oysters

Oysters are another type of seafood that is high in nutrients and vitamin D. Oysters, a type of saltwater clam, are low in calories and contain about 320 IUs of vitamin D. They also have a higher concentration of vitamin B12, copper, and zinc than a multivitamin tablet. Fruits contain significantly less vitamin D than seafood; therefore, if you are a non-vegetarian and enjoy seafood, raw oysters and salmon are the best sources. Adding boiled oysters to your salad will not only add a lot of flavor but also a lot of health benefits.

Mushrooms

Except for vitamin D fruit juices and milk, mushrooms are the only plant-based foods high in vitamin D. When exposed to sunlight, mushrooms, like humans, synthesize this vitamin. However, not all mushrooms are beneficial because the majority of them are grown in the dark and lack the necessary vitamin. You can incorporate maitake and portobello mushrooms into your diet. One cup of diced portobello mushrooms may have 400 IUs of vitamin D. Mushrooms can be added to soup, pasta, or stir-fried in butter and garlic.

 Milk

A large glass of milk contains up to 100 IUs of vitamin D, while a bowl of yoghurt contains approximately 80 IUs. The amount can vary depending on how much fortification is added to the milk or yoghurt. Milk substitutes for vegans and lactose-intolerant people, such as soy milk and rice milk, are also fortified with vitamin D, and the amount is listed on the label. Vitamin D fruits, milk, and whole eggs are all excellent alternatives for vegetarians who cannot consume fish. A glass of milk in the morning or adding it to your smoothie is an excellent way to get vitamin D into your diet.

Eggs

Whole eggs are a good source of vitamin D in addition to being high in protein and nutrients. If you don't want to rely solely on fortified vitamin D fruit juices, you can eat eggs. However, keep in mind that the protein in an egg is found in the whites, while the minerals, fats, and vitamins are found in the yolks. To get that dose of vitamin D, you'll have to eat an entire egg. Eggs are one of the most versatile foods available; you can prepare them in a variety of ways each day to meet your vitamin D requirements.

 

Orange Juice

Although natural sources of vitamin D are limited, some commonly available foods are fortified with this nutrient to ensure the body meets its daily requirement. Around 75% of the world's population is lactose intolerant, and 2-3% have a milk allergy. Not to mention that many people are vegetarians or vegans. As a result, packaged orange juice in many countries is fortified with vitamin D and other nutrients such as calcium to ensure that you meet your vitamin D requirements.