There are several causes for brown spots on your hands, not all of which have to do with a vitamin deficiency. Brown spots may be due to a lack of vitamin C or B12, anemia, weak liver function or cumulative sun damage. It's important to investigate each potential cause; your doctor can help. If your brown spots are indeed caused by a lack of essential nutrients, add a vitamin supplement to your daily routine, and increase the amount of fruits and veggies you eat---prime natural sources for a host of all-important vitamins and minerals.
Lack of Vitamin C
You might remember scurvy as a disease that primarily affected Renaissance-era sailors confined to a ship for months at a time. Although it's rare now, scurvy does still appear in malnourished adults. It occurs when people don't ingest enough vitamin C, a vitamin the human body isn't capable of synthesizing on its own. Scurvy symptoms include bleeding gums and small, dark spots on the skin. The hair that grows out of these patches is curvy and shaped like a corkscrew.
Lack of Vitamin B12
According to a 2008 joint study performed by India's Saveetha Medical College and Singapore General Hospital's Department of Family Medicine and Continuity Care, vitamin B12 deficiency can cause skin discoloration and lesions---without any other symptoms being present. Vitamin B12 deficiency can cause "cutaneous manifestations," including "hyperpigmentation"---an overdose of color in the skin, like that of a lesion or brown spot. When these manifestations occur on the hands and feet, this study says vitamin B12 deficiency should be investigated as a cause.
This type of anemia is genetically inherited---it's not the type of anemia that occurs when your body runs short of iron. In this case, the body can't produce enough red blood cells, white blood cells or platelets. A primary symptom of the disease is brown spots on the skin.
Weak Liver Function
Your liver is responsible for absorbing nutrients from the food you eat, as well as ridding your body of toxins. You may have heard discolored patches of skin referred to as "liver spots"---this can be an accurate description in some cases. The liver helps filter your blood, removing harmful chemicals that contain free radicals, elements that cause skin damage on a cellular level. If your liver isn't doing its job, several external signs revolve around your skin: rashes, itchy skin and brown spots.
Flat brown spots, or lentigines, may be the result of sun damage that occurred earlier in your life. They're most often seen on the face and hands, appearing during middle age. They can fade on their own if your skin is protected from the sun with clothing and sunscreen, or you can have them treated with lasers or peels. You'll have to watch these spots carefully to make sure they don't change in color or shape; if they do, they could be a form of skin cancer and should be inspected by a doctor immediately.