It is very difficult to pin point if a person is suffering from vitamin deficiency because you can suffer from various symptoms which are a result of not eating enough nutritious healthy food. However even after eating healthy food it has been seen people suffering from deficiency that is because some vitamins are not present in adequate amount in our food. Such vitamins need to be gained from external source. Food source alone is not adequate to get the vitamins. Vitamin D is one of them. Usually our food does not contain enough vitamin D. 

Vitamin D is naturally present in very few foods. Good source of Vitamin D is flesh of fatty fish (like Salmon, Tuna, etc) and fish liver oil; moderate amount in beef and chicken liver, cheese and egg yolks; and very small amount in mushrooms.

Another good source of Vitamin D is exposure to sun; most people meet some of the Vitamin D needs through this source.

Dietary supplements and fortified food are good source of maintaining Vitamin D levels. Fortified food like milk, yogurt, cheese and Kellogs cereals has adequate amount of Vitamin D.

Who may suffer from Vitamin D Deficiency?

You may not get enough Vitamin D if:

• You don't get exposed to enough sunlight. Usually you would be able to get all the Vitamin D if you expose enough bare skin to morning or milder sunlight. However it is difficult for some people to get enough exposure during the winter.
• You don't eat fish and meaty food. Its difficult to get all required amount of Vitamin D from only vegetarian food.
• You don't take supplements or eat fortified foods.
• Your body needs more vitamins than usually especially during pregnancy and after delivery.

Some Warning Signs of Vitamin D Deficiency to Remember

• Muscle Pain and Body aches - This symptom will be commonly seen in your and my life. We all get body aches and muscle pain. If you feel tired and fatigue due to muscle pain and body ache , do not neglect it. The chronic fatigue can be due to Vitamin D deficiency. Most of the time people are unable to sit ot stand for longer time due to fatigues.
• Digestive Problems - Vitamin D helps to maintain the useful bacteria level in our digestive system, hence the lack of Vitamin D leads to poor digestion and other problems like bloating of stomach, and constipation.
• Sweaty Head - Do you sweat a lot on your head? Along with sweaty head, if you also have the other symptoms of Vitamin D deficiency, you may be suffering from low Vitamin D. Sweaty head can be due to lack of Vitamin D as it is one of the classic sign of its deficiency.
• Happy and Sad mood - Vitamin D is essential to keep up the Serotonin level, which is responsible for inducing happy feeling in you. With low level of Vitamin D, you will be always depressed and sad.
• Joints and Bone issues - Along with Calcium,  Vitamin D is also very essential to maintain the strength in bone. Low vitamin D level mainly affect the joints in children and older adults. Fragile bones, knock keens, or bow knees are the classic signs of low Vitamin D. Extremely low level of Vitamin D leads to Rickets (bow or knock knee) in children and Osteoporosis (softening of bones) in adults. Hence these people are more susceptible to fractures.  

How to prevent or avoid Vitamin D Deficiency?

• Eat all variety of food. Eat adequate quantity of vegetables, meat, fish and eggs.
• Add fortified milk and ready-to-eat cereals in your diet. Eat at least 1 cup of cereals with milk every day.
• Some brands of yogurt contains Vitamin D. eat those kind of yogurts every day.  
• Daily exposure to sunlight if possible. Usually in winter its not possible to get enough sunlight. During those days add extra fortified food or take supplement.
• If Vitamin D is extremely low then medical treatment or supplements are necessary. Contact your physician immediately for the same.
• If you notice above warning signs do not wait long, get yourself checked by a doctor for Vitamin D deficiency.
• Pregnant women should include Vitamin D fortified food and supplement even though there is no symptoms of deficiency.