Why breast milk is not enough
According to the CDC, breast milk alone does not give a baby enough vitamin D. That is why drops are recommended for breastfed babies. A lack of vitamin D can lead to rickets, a disease of growing bones. Turkey's guideline notes that low vitamin D is the most common cause of rickets.
US and UK advice
The CDC and the American Academy of Pediatrics recommend 400 IU of vitamin D a day for babies who get only breast milk. The same applies to babies who get both breast milk and formula. Drops start in the first few days of life. In the UK, the NHS recommends 8.5 to 10 micrograms a day for breastfed babies from birth to 1 year. This applies even if the mother takes a supplement herself.
Formula-fed babies
Infant formula has added vitamin D. The NHS says babies who drink more than 500 ml of formula a day should not get extra vitamin D. The American Academy of Pediatrics recommends drops for babies who drink less than 32 ounces (about 950 ml) of formula a day. As you can see, the cut-off differs between countries.
What Turkey does
Turkey's Ministry of Health guideline asks that every newborn gets vitamin D, however the baby is fed. Drops start on the first day of life at 400 units a day. They continue every day until the end of the first year. The Ministry supplies the drops and family doctors hand them out. The guideline says higher preventive doses are not needed in the first year.
Too much of some vitamins can be harmful. Do not raise the dose on your own, and do not give two supplements at the same time. Your doctor decides the right amount and duration for your baby. Bring your questions to your next check-up.