To solve this optimization problem using Gurobi, we need to translate the given objective function and constraints into a format that can be understood by the Gurobi solver. The objective is to maximize a complex function involving milligrams of vitamins D, B4, and B12, subject to various constraints related to cardiovascular and digestive support indices.

Given:
- Variables: `x0` (milligrams of vitamin D), `x1` (milligrams of vitamin B4), `x2` (milligrams of vitamin B12)
- Objective Function: Maximize \(4x_0^2 + 7x_0x_1 + 5x_1x_2 + 9x_0 + 6x_2\)
- Constraints:
  - Cardiovascular support index constraints for each vitamin
  - Total combined cardiovascular support indices with various minimum and maximum limits
  - Total combined digestive support indices with maximum limits
  - Variable type constraints: `x0` can be fractional, `x1` must be an integer, `x2` must be a whole number (integer)

Below is the Python code using Gurobi to model this optimization problem:

```python
from gurobipy import *

# Create a new model
m = Model("Vitamin_Optimization")

# Define variables
x0 = m.addVar(vtype=GRB.CONTINUOUS, name="milligrams_of_vitamin_D")
x1 = m.addVar(vtype=GRB.INTEGER, name="milligrams_of_vitamin_B4")
x2 = m.addVar(vtype=GRB.INTEGER, name="milligrams_of_vitamin_B12")

# Objective function
m.setObjective(4*x0**2 + 7*x0*x1 + 5*x1*x2 + 9*x0 + 6*x2, GRB.MAXIMIZE)

# Constraints
# Minimum total cardiovascular support index from milligrams of vitamin D and B4
m.addConstr(8*x0 + 6*x1 >= 4, name="min_cardio_support_D_B4")

# Minimum total cardiovascular support index from milligrams of vitamin D, B4, and B12
m.addConstr(8*x0 + 6*x1 + 4*x2 >= 5, name="min_cardio_support_D_B4_B12")

# Maximum total cardiovascular support index from milligrams of vitamin D and B12
m.addConstr(8*x0 + 4*x2 <= 27, name="max_cardio_support_D_B12")

# Maximum total cardiovascular support index from milligrams of vitamin D and B4
m.addConstr(8*x0 + 6*x1 <= 17, name="max_cardio_support_D_B4")

# Maximum total cardiovascular support index from milligrams of vitamin B4 and B12
m.addConstr(6*x1 + 4*x2 <= 21, name="max_cardio_support_B4_B12")

# Maximum total cardiovascular support index from all vitamins
m.addConstr(8*x0 + 6*x1 + 4*x2 <= 21, name="max_total_cardio_support")

# Maximum total digestive support index from milligrams of vitamin D and B4
m.addConstr(3*x0 + 2*x1 <= 15, name="max_digestive_support_D_B4")

# Maximum total digestive support index from milligrams of vitamin D and B12
m.addConstr(3*x0 + 7*x2 <= 22, name="max_digestive_support_D_B12")

# Maximum total digestive support index from all vitamins
m.addConstr(3*x0 + 2*x1 + 7*x2 <= 22, name="max_total_digestive_support")

# Optimize model
m.optimize()

# Print solution
if m.status == GRB.OPTIMAL:
    print("Optimal solution found:")
    print(f"Milligrams of Vitamin D: {x0.x}")
    print(f"Milligrams of Vitamin B4: {x1.x}")
    print(f"Milligrams of Vitamin B12: {x2.x}")
else:
    print("No optimal solution found")
```